Interesting. I do IT infrastructure support. I generally respond after I've completed the task but this makes me think that I should reply to their email immediately with something like, "I'm looking into this."
I managed an IT team for awhile. While you may be working diligently on the task, the 'client' (whoever that is) has no idea that any sort of action has even started, which can induce a lot of anxiety, depending on the situation. You'll have much happier customers if you keep them in the loop early.
It doesn't have to be arduous. The four words you wrote above are enough. Or, "Hi Bob, I'm on another task at the moment, but I should be able to look into this in a couple of hours. Will be in touch." has a significant calming effect, and will often buy you extra time.
Of course, Bob might just say "this can't wait a couple of hours" but that's a separate chapter in human relations. :)
