I've heard ZRAM mentioned before and I've just spent 5 minutes reading articles on it... Which is about the maximum I have time for these days when it comes to esoteric linux internals.

What's the downside? Does it use much CPU?

If I have enough RAM already, should I still enable it?

One article says it can be mapped to /tmp to reduce i/o. Is that a good idea?

This article is light on all of these kind of details.