I think the idea is to treat employees you pay as if they where doing it for free. Say you give a boring task that’s not meaningful to a volunteer they’ll just up and leave as they won’t gain anything from it.
It's okay to have boring work. It's challenging to _only_ have boring work.
In this case, a volunteer is a nice mission-less proxy. Is some work engaging for the owning employee, or do you need to get someone else on it, or even switch to outside staff for it?