@JB iirc yaourt effectively wraps pacman, so you can use it everywhere you would use pacman and it'll get official packages when they exist.
As far as installing everything from the AUR, it's not vetted like the official repositories so it's kind of like sideloading an untrusted app store onto your phone. Realistically you probably won't run into any issues, but theoretically code from the AUR can't be trusted.
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