I will never delete anything. By time you jump in as a creator (Audio/Video) you should understand that storage & backup are investment.
Youtube did not provide us to download original content of our videos uploaded. And if you ripped from online downloader, etc the resolution & codecs are poor.
So my suggestions: Always Render in Highest quality original resolution available on your software, Make it as ‘Master’, Keep it!
then Encode to Youtube 1080p H264 MP4, this what you’ll upload to YT.
Anytime you want to clear space, You delete only the Project Files, Render Files, Cache Files,, But Not the Masters.
For my TV commercial works, usually i gave my clients 3 months period to keep the files after it was aired. after that i’ll delete it.
Or I give them the whole project files and Masters. If they want to re-work, revised, etc, there will be an additional cost.
My YT are personal & commercial work for Music. I have 12TB of Storage since 2012
All my clients project are there too.. the space will keep growing.. just be prepared. Or the worst, storage failure.
1TB of external harddrive are considerably cheap these day. Buy one every 6 months or a year you should be good.