[franciscop]

It might work for static sites, but as soon as you start to get fancy and use JS+CSS correctly [tm] it's more difficult because, as you say, there will be state classes modified with JS which changes the style but wasn't previously displayed.

That said, my point still remains the same time invested in learning+using+tuning uncss would probably be better spent on any of my points or some others suggested here. AFTER that, sure! I got the whole page for the library I linked down to 10kb in TOTAL including images [in svg] for a competition. It has gained a bit since then though, mainly with analytics.