I think that is an excellent question.
I've only just recently noticed for example that (say) Spywareblaster needs running on each account to protect the PC.
My understanding is that any 'scans' will scan the PC covering all users.
Dell XPS 13 9370 (2018) review
No need to scan sketches into your computer with Moleskine's new smart pen
Streaming : Netflix ou Amazon Prime Video ?