Work profile: I can split my works stuff and personal very easily (and for security as personal apps cannot see or work with work stuff usually).
This also helps if you want to get same app installed multiple times. Ex. I could install pokemon go and use two profiles same time with split screen.
“true” secondary profile: like in desktop OS where you can create multiple profiles, this will “boot” phone to new profile and it has own partition and apps. Cannot interact with other “true” profiles.
I use that with my child if I hand phone to her. She cannot get to my stuff (not even images or other data) and only has her stuff available.