packages to clean build. none, all, abort, installed, not installed, what is the correct way(best) to install?
I might chip in, waiting for the more expert users offering a broader view…
Normally I tend to clean build already installed programs either when explicitly suggested by the package maintainer (eg. certain VPN clients, TOR browser,… I think it might probably linked to the nature of the package and the trust signatures those are linked to, but that’s just a supposition), or when a change in the building libraries makes the old built program not working anymore - that happened, for example, with a major update in GLib/GCC/a unicode language library I am forgetting at the moment/...
I would assume that all would be your best bet. I’ve said none in the past but when thinking about it some packages are probably rewritten in some context so that the new changes will become effectual. I do all now ‘all’ the time and haven’t seen any deleterious effects on my computer system and OS.
Rich 
just a thought, option ‘‘none’’ is the same as chaotic aur, just prebuilded program by someone else?
I don’t use chaotic-aur, but, as far as I’ve understood, if you don’t clean build, the package should be simply delta-updated like it happens with regular packages, while with clean building yay erase the old cache relative to the package in question and it downloads the sources again.
Ive just found this thread from 2022 where a similar question was asked, as a reference 
if you see, there you have three different approaches to your question, so, except for some cases where it’s necessary - two of those are in my previous message -, you can decide a strategy yourself…
sorry if I wasn’t that clear in my explanation
ah, i missed that thead, was reading it now and kinda agree with Kresimir with the reasoning(‘‘all’’). but it seems that ‘‘none’’ is also fine…
In general, I would recommend choosing none which is the default.
If a build ever fails, then try again choosing the specific package or all.
Building will often be faster if existing files can be leveraged however sometimes it will cause conflicts.
For me, not cleanbuilding is fine 99% of the time.