How much CPU cycles pre-compressed css/js files can save?

The solution to use pre-compressed gzipped css/js files is claimed to save cpu cycles.

I am suspicious. To me, if web server is not caching the gzip file but compress and serve on every request, that be crazy and why.

So even I am asking how much cpu cycles this pre-compression can save? But truly, I am also asking if this is really saving cpu cycles at all? ( maybe in the early days?)