I was driving sims before I first started karting. It definitely helped, but I still had to learn everything - it just made the learning process a bit faster, because I already knew what countersteer, understeer and oversteer was, the basic concepts of grip and apexes, etc. But it definitely didn't stop me from going "woah, that's fast" and backing off the first time I went down the straight at 60.
At this point in time, after 2 years of instruction from a team of coaches, simulators hold very little value for me in terms of learning things. They keep my skills from degrading too much during the off season, and iRacing will help me to learn new tracks, but other than that I would rather have 10 laps of real track time than 100 laps of a virtual track, heck maybe even 1,000 laps. In terms of learning setups, the changes I will be making in real life will be too fine to feel in a sim, the range of limit in real life is too narrow to consistently hit in a sim without the G forces, and the racing is too close in real life to be able to keep it clean in the sim with the lack of situational awareness that you have on the computer.
For the record, I'm quite fast in real life (
check my videos), just as fast as my coaches, hand-picked by Jim Russell, and when I went to do a high performance course in road cars at Skip Barber the instructors there were highly impressed, but in sims I've never been able to get that 'nth degree out of the car, so no, I don't believe that skill is transferable. You can learn things about the virtual world from racing in real life, and you can learn some things that you would learn in real life with virtual track time, but being fast in real life and being fast in a simulator is about as related as being fast in a NASCAR stock car and being fast in a Formula car. Some people are naturally gifted at both, most people are good at one and not so good at the other. Look at many of the professionals who use iRacing - some are very good, yes, but some are quite mediocre or even bad.