No the optimizer does way more work than just caulk out unseen faces, it optimizes geometry and triangle output, and a bunch of other things. If it wasn't needed I'm sure ID would have just told us to make sure to caulk everything and would not have built an optimizer. I build exclusively in Caulk texture anyways, and only texture faces I need to. This helps, but on some maps it doesn't matter how much you pre-optimize the DMAP process can still take 10 minutes like it used to for my Cathedral map. That is until I changed most things into func_statics.