every software update is at least 50MBs nowadays so i got to thinking where these files actually go after they've been installed. is there a way to remove these files? i reckon there shouldn't be a problem since they've already been installed?
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The only thing they leave on your system is a small file in /Library/Receipts/ that's used by System Updater to check which updates have been applied.
Receipts do more than that. Each receipt mirrors the structure of its associated application. Whenever permissions are repaired, the repair utility refers to the receipt for proper permissions settings.