Here's my two cents worth.
ADY and IDY, the instant part of IDY is in reference to the rate of hydration for the yeast. IDY hydrates more quickly than ADY, this is why it can be added to the dough without prehydration, this is also why it tends to tolerate cold water hydrating better than ADY. The whole thing about prehydrating yeast is to minimize the flushing effect of cold water entering into the yeast cells and flowing out, bringing with it the plasma material from within the yeast cells (glutathione). When this happens, the yeast cells are not killed, but they don't ferment nearly as well as sound yeast cells do. Also, there is a reducing (softening) effect upon the dough from the glutathione. This may not be seen as readily by home pizza makers as it might be interpreted as just a little too much water, but in a pizzeria or other large production facility it can mean difficult dough handling properties, or even collapse of the dough at some point. Is it absolutely necessary to prehydtrate IDY or ADY in water at specified temperature? In home made pizza dough, the answer is no, will it hurt anything if you do prehydrate it? The answer again is no. So what is the benefit to prehydrating ADY and IDY? The answer is better, overall yeast performance and consistency. How hard is it to get a small amount of water at 95F for IDY or 100F for ADY? Not hard at all. Just remember that both of these temperatures are at near skin/body temperature, it only takes a minute, actually, just a few seconds.
Tom Lehmann/The Dough Doctor