Mmm... it was fun for me when I started playing, but then it just got in the way of me actually learning a song. I play Rocksmith to learn songs rather than having to use a boring tab on Guitar Pro, and with DD lowered down you're not actually learning the song, you're just playing some notes of the song. Whether you have fun playing half the song or not is up to the player I guess, but for me the way to go is slow down difficult parts, and speed it up as I learn it. I guess a beginner can lower the difficulty and play a very difficult song, but in the end he's not really playing the song anyways. I'd say the best strategy to learn and practice is slowing things down and playing them over and over until you get them. For example, scale exercises, you start out very very slow and then you start going faster and faster and that will help you with your overall playing. If you grab that same scale and play out of the 30 notes 5 notes... you're not doing anything in my opinion.