Using the blocks stinks out here in the west coast, especially at many state and national parks as the ground is rarely level. It can be down right "slopey" at times although I don't think that is a real word :) If I ever buy another RV, it will have auto leveling jacks for sure.
I typically use them under both tires in the back when leveling my 24ft class C. I can't say for sure if it's better for the RV but I have to imagine that it has to be a little safer that way. Those blocks are only made of plastic and more is better in my opinion.