Well, I guess if you use a lot of front blocks under the front jacks, than you need to be super careful. Personally, I dont use blocks, except maybe 1 inch pads, if I think the surface is soft. JT STrongarms, etc are the best way to keep the front jacks from swaying.
I suppose if your front jacks are not long enough (which is weird in itself, especially on flat ground), than maybe blocks are necessary. But I have seen this situation many times, and always wanted to walk up the campers and tell them about JT STrongarms (or other brands).