I'm only doing a few things on machine with around 32GHz worth of processing power (# of processors * GHz) that I couldn't do on my 80486 running 33MHz with a few MB of RAM. Emacs starts up a little bit faster. Pages in Chrome are more interactive than in Lynx, Mosaic, or Netscape. My word processor fits more text.
On the whole, that 1000x increase in performance mostly bought the ability to have most of the code that runs be interpreted or JITed rather than statically compiled, to play videos, to do some heavy numerics and graphics (including things like family photos and videos), and so on.
It's hard to think of anything I really /need/ in a life-or-death sense or an economic-survival sense that couldn't be done on older hardware with appropriate software. There's a ton of things I want, that help, or where migrations would be massive projects.
If computers were to entirely disappear, and I couldn't automate things, communicate digitally (emails, messaging), word process, write code, I think that'd be a major systemic-collapse-level implosion of society. A lot of people would simply die.
On the other hand, if computers were to regress to 33MHz-level performance, Youtube isn't sticking around, but we'd likely adapt as a society with some structural change, but without such a collapse.