I am a hard core FSX sim pilot, I realize it cannot teach you the feel of the aircraft, but for systems, navigation, and sight picture, I think it can help if you have experience in a real aircraft and can understand the differences.I have the PMDG 737NGX with FS2 crew and I blew an Alaska pilots mind with the stuff I knew about the 737-800 even reciting the after takeoff checklist to him, so sims I think can be an advantage if you understand the limitations, but with that said,I have learned stuff that you cant get from a book. I think used correctly can be a valuable tool.