@scowei Asset CleanUp, as its name suggests, allows you to declutter the CSS/JS that is useless in your pages, this being its main purpose. Things like minification, caching are done by Cloudflare which are great. I found it to be a useful service that I recommend as long as it’s used the right way. For instance, if you use “Cache everything” without special page rules, it will also cache logged-in admin pages and they will be visible to guest users as well. They could see the top admin WordPress bar, things like “Hello, [admin name here]!”.
See this article: https://support.cloudflare.com/hc/en-us/articles/200172366-How-do-I-cache-everything-on-a-URL- check the “Important” part in bold.
If you asked me this question, perhaps you thought Asset CleanUp is a caching plugin. No, it doesn’t do any backend caching (although it has some feature such as minification and concatenation like other caching plugins). It works together with a caching plugin. You remove the CSS/JS “crap” and make your page lighter, you minify and combine the remaining loaded files and then you use the caching plugin (e.g. WP Rocket, WP Fastest Cache etc.) to cache the final HTML source code ??
Hope it helps and I wish you would find this plugin useful in your projects!