If you look at the pull requests this seems to be the case with bitcoin too... however the bot doesn't seem to build trunk + all pull requests at once, only trunk + single pull request.
Yes, combining many pull requests is not trivial and requires a real human to do.
I'm not too sure what to test with these binaries though, maybe if I "need" 2-3 features I can save on building time?
Well, the idea is you can run it as your ordinary everyday client (with the awareness that it has a lot of untested and potentially broken code) and maybe hopefully stumble upon some bug we're not thinking to test for explicitly.