tl;dr: You'll lose maybe as much as 10% of your charge overnight if not plugged in, and the first 15 to 20 miles would cost double the amount of energy.
Most people charge every night so you always have an 80% full battery whenever you want to go somewhere. If you left it unplugged on a very cold night, you could lose maybe as much as 20 or 30 miles off the rated range due to the car using electricity to run the battery heating system to prevent any damage to the battery.
There are a lot of variables, the most important of which are how far you plan to drive, whether you pre-warm the car while it is on AC power, and how you drive it.
The standard 80% charge for the 85kWh battery is about 230 miles. That range translates to an average consumption of 290 Watt hours per mile. If you jumped into the car on a cold morning and just started driving, you would probably be consuming upwards of 400 to maybe even 500 Wh per mile for the first 15 to 20 miles as both the battery and cabin were heated. After that, things would taper down and you could easily hit 300 Wh per mile for the rest of your trip. A bunch of starting and stopping such as running errands would make that worse because it would take longer to heat due to the cool-downs when parked.
If you had it plugged in overnight and in the morning, you used the smartphone app to turn on the cabin heater though, it would use your AC power to not only heat the cabin but also start warming up the battery. Then, when you actually started driving, you would already be at that 300 Wh or so average.
We have never had any issues with not having enough charge to go somewhere, even on the occasions where we forgot to plug it in overnight. Our typical daily errand trips can be between 15 and 40 miles.