I presoak 11x14" and 8x10" sheets to be processed in pyro developers and find I get more even results that way. I also presoak East European films that have a blue-green anti-halation layer, because the dye comes out better that way, and doesn't seem to come out at the fixing or washing stage, like the magenta T-max dye.

I wouldn't use Photo-Flo in the presoak or developer, though I've heard of this practice.