I like using cast iron pans for searing meat since they have a large thermal mass and you can get them ripping hot without damaging them. Being able to put them in the oven is also nice for meat and such. I also use them on the grill sometimes e.g. for making fajita veggies without smoking up the house.
I often want to de-glaze the pan after cooking the meat to make a pan sauce. I have had issues sometimes if the sauce is too acidic the seasoning starts flaking up.
I don't understand how people cook eggs in cast iron. I have an antique cast-iron pan with the smooth surface and a pretty good seasoning but it's not even as nonstick as my crappy old ceramic non-stick pans. I do like my eggs to be very soft and delicate but maybe its okay for crispy fried eggs.
Overall I think it's worth having one since they're cheap, even though they're only really great at a few things.