Welcome to the forums. They're awesome, especially Rounik! Yeah, basically Rounik explained BEAT MAPPING in a nutshell there. I basically use Beat Mapping when I record my drums in a studio. No drummer is ever 100% on the click/metronome! It's impossible! That is called a drum machine! hahahahaha:) Anyway, when you beat map the kick and snare drum, for example, you're basically moving Logic's time grid to match your "actual" playing so that you still keep the original feel of the drums that you recorded. Now anytime you want to add any kind of loops to your new beat mapped kick and snare parts, those loops will automatically line up, IN TIME, with your drums, and after that, any other parts (bass, keys, etc.) can be added in time to your beat mapped drums. If you don't beat map your kick and snare, for example, and then you want to add loops to your drums, you will notice that they aren't quite in time with each other, soooooooooooo, ya gotta beat map the drums:) Steve H mentioned in his 201 tutorial that he actually likes doing the physical labor of lining up the beat maps, and I have to say, I do too:)
Does that make sense?