Hi there @newbie24689!
To be fair, I didn't write the documentation (I'm just a moderator), but:
Using a secondary profile for regular usage allows you to make use of the device without decrypting the data in your regular usage profile.
makes sense to me.
As @mythodical said "make use of the device" sounds intentionally broad there, and I do think it makes sense to prhase it that way.
Example: You could have a secondary profile where you install all of your apps, store your data (contacts, photos, videos).
You can have that profile fully locked and its data inaccessible, but still receive and make calls through the owner profile, use the browser, or anything else.
The advantage of this setup is that you can for example hand your phone to someone else after ending the session of your secondary profile, and they won't be able to access anything in there. If all of your apps/data is in your main profile, they can simply switch from whatever profile you're on when you hand them the device back to the owner profile, and thus access your data, as the owner profile needs to be unlocked for any secondary profile to be usable.
I hope that this provides some more context and perhaps makes that sentence in the docs a bit more clear.