RS lets you slow down a song (or any part of it), and decrease or increase its difficulty level. RS will automatically increase the difficulty as it senses your progress.
I will never play in a band, doubtful that I will even ever play with another human. There is just something about RS that makes me feel like I am actually playing with a band and for some reason I can actually hear how what I am playing fits into the song. By scoring your achievements, it shows you how sloppy you really are!
Yes, there are flaws with the simulation (RS is not a game!) that I wish they would fix; but all in all, for me, I am having the most fun that I have had since I started playing a guitar. Imagine a 65 year old man head banging to Iron Maiden's Trooper!!!!