If you're a "doer" (for example, a developer) your to-do list for today is likely to have three or four items on it - each a couple of hours in length - and context switches (interruptions, changing task) are expensive (half an hour or so).
If you're a manager, your to-do list is actually about a hundred items long - but each item only takes a few minutes to complete (also meaning that it's probably not written down and it's hard to enumerate what you actually did today). And most importantly - context switches are cheap.
So reviewing someone else's work is actually only a ten minute job (it doesn't need to be detailed - just check to see if it fits with your philosophy).
But for a developer that's ten minutes plus an hour of context switching - making it very expensive.
For a manager that's ten minutes, plus a minute of context switching - making it cheap.