Well... its basically just a time-saver, that's all. Since I don't consider the days-weeks-months-long search for ore veins to be the "fun part" of a GT modpack, I tend to short-circuit the process a bit.
What happens is, I begin a new pack play-thru, but it takes so darn long to get into mid-game that I (literally, no pun intended) run out of steam by the time I get there. So I never get to experience mid-to-late game, but I play thru the early game over and over and over again.
So it's just kinda nice to be able to fast-forward thru a bit of the early game by taking some shortcut advantages of the tools available. I still do everything manually - for instance I just made a little slime farm because I cheated to find a slime chunk... however I didn't just use creative mode to give myself slimeballs, I still did the work to make a farm for them. It's cheating, yes, of course, but only to a certain point. We all must determine where that point is, for ourselves. It's our world, we can do what we want.
I always use Tin Ore as my example - if I didn't use CoFH clearblocks to find some tin deposits, I can almost guarantee it would have taken me at least a full week (of real time, real days) before I ever sniffed some tin in my world. I would have spent a full week doing nothing but exploring for the required tin. When I finally found where the tin is hiding, there's no way I ever would have just stumbled across some of it. And that would have left me very frustrated at my lack of progress in the pack.