I used MSFS like every day in high school and college. Actually, when we bought our first computer, my Mom said I could get one game to take home with it. What did I get? MSFS 5.1! From there I had 95, 98, 2000, and 2002. Got tons of add-ons with it too. Stopped playing it much after my junior year in college. Now, don't play it at all. I was thinking about re-installing it, we'll see.
I never really used it for anything more than fun. Flying the 757, 767, L1011, 727, 737, DC-9, etc... downloading all the panels, sounds, and other stuff. It was a hobby, and a fun one at that. I wouldn't really fly cross countries or anything. Just take off from ORD, fly 50 miles away, turn around, do an approach and land. Lots of takeoffs, landings, and ILS approaches to mins. Downloaded some of the old DC-2s, DC-3s, and Connies in TWA scheme and did harrowing approaches to mins using range and stuff. Lots of fun.
I'd think of it less as a "training tool" and more as a great way to have fun flying around doing some of the "fun" stuff that you wouldn't otherwise get to do for years... like shooting a CATIII autoland in a 767-300ER at JFK, then pulling up to an add-on terminal that is picture perfect. Even doing that stuff will help you grow your aviation knowledge to a point. Just don't try and use it for something it's not... and don't let it interfere with your real training.