Rolling pin technique

Hi! When I read up on croissant making, I sometimes come across tips specifically about rolling the dough (during the folding stages) "from the middle out in each direction" - that is to say, not from edge to edge. I have no problem understanding the procedure, but I don't understand why this is important. Why would it make a difference as long as the dough/butter block is uniformly lengthened? And when you use a dough roller to do the rolling, isn't it doing just that; rolling from one end to the other in one go? 

Sorry if I'm missing something obvious here. I'm still on my quest for really good croissants, and since the crumb structure is my biggest hurdle I want to understand the things I'm reading. If I do, there's a slightly bigger chance of actually getting somewhere. Currently, I'm trying to adopt the motion and swiftness of a dough roller, being careful to apply the same pressure on both sides of the rolling pin and really aiming to elongate the dough quickly rather than letting it get warm. I don't know how much rolling pin technique influences the crumb structure, but if you have any golden tips you're most welcome to share.