I've tracked my car for 5 years, then started racing for the past 5 years, and moved up to pro racing two years ago competing in Pirelli World Challenge and MX-5 Cup.
The simulators today are fantastic. The skills you learn in the simulator are 100% transferable to real life, and they happen without you having to think.
I went 9 years without using a sim and then two years ago started using it.
What gets transferred immediately are how you turn the steering wheel, catching the car in slides, and your gas pedal application while this is happening.
People often forget that our bodies are complex operating systems and they are operating distinctly. There is plenty of documentation that shows mirroring for knowledge transfer works, and when you use a sim the habits that you develop are available subconciously to you.
I'll give you two examples, the first is at my last race in Global MX-5 Cup at Laguna Seca. At the start of the race on the opening lap I was going through the corkscrew and got hit at the apex of the right hand corner. The car immediately went into a large slide because of how much steering input I had. I immediately started to correct with both steering input and gas pedal application. I had to correct the two slides to save the car. Immediately upon impact my body was doing what I needed to do, it was completely subconscious, so much so that the only conscious thought I had was, wowee fun, just like the simulator. There was no fear, despite the fact that the slide was massive and I was likely to hit the wall if I didn't catch it.
The second happened a couple of months earlier. I was testing at Sonoma in my BMW m235ir for a Pirelli race. I was going out on old tires, that we were going to swap for fresh ones at the next session. Going through the double right hair pin, I applied a bit too much throttle, car started to slide, I was correcting, but under corrected and went back to full throttle too soon. The car spun, hit the wall, caused $10,000 in damage. The reason that happened was whenever I played the sim I always kept my foot in the gas. Just trying to save the car and have fun. Then I realized, that when I use the simulator I can't approach it from a "fun" mentality, because my brain is remembering what I'm doing. I have to treat it like real life, or I will do something stupid in the car.
There are certainly differences between how a real car handles and a simulator handles, but the skills are the same and what you are really honing is the ability to control the car which is completely transferable. The brake points are very transferrable so it is a great way to push yourself in a simulated practice to get ready for a real race. Learning the track is obviously a benefit.
iRacing has done a fantastic job at all of the above. Coming from a tech background I'm actually blown away by the realism and how much it teaches you transferrable skills.
If you take one of the top 5 people in iRacing that's never been in a car before and put them into a race car they will be quick. This is because everything that will be happening they have already trained for. They won't have fear because everything will feel the same. As long as you don't have fear, and have the underlying skill, subconsciously you will do what you need to.
The reverse isn't as true. Being quick in real life doesn't mean that you will be fast in the simulator. This is simply because it can't replicate the physics 100%. In iRacing it is very sensitive to understeer as you enter a corner, where in real life you can get the car to slide a bit more with some hard inputs into the steering wheel.
But overall I would say it is a 90%+ effective tool, so much so, that anyone who isn't using one in pro racing today, is really at a disadvantage.
The other thing that is critical to racing is practice. Any sport you take seriously the more time you spend doing it the better you will be. Unfortunately racing is extremely expensive, and so no one but the absolute pros can spend as much time as they would like in a race car. Being able to hop on the simulator, at any time, is amazing to help you continue your training and stay sharp during the offseason, or at times like this when all racing is pretty much cancelled.
Anyone who is saying that this isn't transferrable is simply incorrect. They've already taken pure sim racers and put them behind the wheel of real race cars and those people did phenomenally well.
There is more strain physically in a real car, g-forces, breathing, pulse will be higher, but these things are much easier to train for.
There is a reduced amount of feedback certainly, one of the biggest issues for me is not getting a great feel for the brake pedal, but this is where muscle memory comes in, you keep doing laps and refining and your muscles will recognize what inputs you need even though the g-forces aren't there.
Furthermore I tried VR iRacing for the first time and it was insane how amazing the VR is. It is completely life like, just missing the rush of air around me.
I was at Road Atlanta doing laps and went through the last corner on my first lap. You come down a massive hill, hit the compression, and turn right into the fastest corner of the track where you also have walls on both sides that are very close. This is not the corner to fuck up. There is tremendous g-forces in this corner in real life. On the way down the hill I feel fine in VR. The second I hit the compression I get dizzy. This is because my eyes and everything around me is recognizing this part of the track and my body is tensing because it remembers real life. But my body isn't feeling the compression. So the difference between what my eyes see, my brain interrupts, and the lack of sensation in my body is making my brain go haywire and makes me dizzy.
The first time I just thought it was odd. The second lap same exact thing happens. The third lap again. It happened every time I had to take the VR off because I started getting a headache.
Anyway those are my real life stories. If there is anyone on here racing or tracking their car I highly recommend they get a great sim and install it in their house. It will be a lot cheaper than tracking and infinitely less expensive than racing and it will tremendously improve your skills.
This is probably less relevant for top of the sport racers, but if you watch today's youngest F1 athletes all of them do sim racing and all of them are extremely quick. Specifically Lando Norris and Max Verstappen.