DoggCrapp and 5/3/1 were both huge for my growth, both physically and as a lifter.
EDIT: Missed the "and why" portion.
For one, if you have exercise ADD, this program is great because you're constantly using new movements. It makes you look forward to the next training session, especially if you structure things such that you have at least 1 movement you are looking forward to in every session, rather than putting all your favorite movements into one session and then trudging through the rest of the program.
The brutality of the method is enticing when paired with that fact that you're doing 1 movement for 1 set (essentially) each day. It's a quickish session, but still effective, and you definitely feel like you got in a workout.
Really, the biggest thing DC did for me is break me out of a lot of dogma. I couldn't go around thinking "only squat, bench and dead matter", because I was going to quickly run out of options that way. I had to start using machines, partial movements, and all sorts of other things I had written off in the past. In doing so, I exposed myself to a lot more movements and figured out some things that would work well in my future training.
This worked in the opposite way of DC. Instead of learning the value of variety and a lot of lifting tricks, 5/3/1 (and specially the BBB assistance work) taught me that effort and volume go a long way in improving physique. Prior to using 5/3/1 I was doing a lot of low volume, high frequency strength training work, and my bodyweight was staying pretty low.
When I started 5/3/1, without even intending to put on weight, I gained 12lbs in 6 months. I tell this story a lot, but the physical transformation was actually so radical that my wife's co-worker, who hadn't seen me since I gained the weight, saw my wife and I out for a walk through the neighborhood and thought that my wife had gotten divorced and started dating again. He did not recognize me at all.