I'm doing a medium-term repair on the results of a long under-sink leak. There's no floor, but a tile-on-plywood insert that sits about three inches above the subfloor had warped, the drywall was in bad shape at the base, and the subfloor itself is a bit rotted. (The heavy cast iron radiator sort of sinks into it at the worst part, for example, although certainly not all the way through.)
It doesn't make sense to replace the subfloor until the next time someone does a kitchen remodel on the house--you'd really have to pull the counter and 10+ feet of of deep custom kitchen cabinets out to make it perfect, and probably the finished floor as well. So I'll replace the bottom few inches of drywall and the insulation behind it, put down some thin plywood or laminate flooring before replacing the radiator (this will spread out the weight and provide some spill protection), and build a new tile insert.
My question is, does it make sense to do anything to the exposed portion of the subfloor before covering it? I've heard people use epoxy ("bondo") or wood hardener and wood filler for rot repairs sometimes. It seems like it would take a lot of filler. Do these actually make the wood stronger, or is the result really cosmetic and I shouldn't worry because the wood will be covered?