I prefer to review my foreign & orphaned packages after an update, for the reasons I outlined above.
If an AUR package blocks a system update due to a dependency issue, the AUR package can be safely removed with sudo pacman -R the-AUR-package, and the update process run again to successful completion.
The AUR package, if the user still wants it on their system, can then be rebuilt against the updated system packages after the update has completed (pamac build the-AUR-package).
But removing foreign packages before an update can cause issues if they have become foreign only due to a name change or another package replacing them. It could result in a vital system package being removed, and due to its removal before the update, the system won’t automatically install the replacement package.