Most companies I've worked for use "I can see them at their desk" or meeting attendance as the primary measure of "your employees are working".

don't they do work you can see?

It's like the adage about advertising: you don't know which ones are effective.

Then you have to get out of all the work you were assigning them yourself. Much better to leave it to a specialist!

Yes, but remember in the scenario you're replying to, you cannot tell if they've done the work. So assigning to the specialist you mention might as well mean tossing the job requests into the bin.