What I find interesting is how many people complain about the number of emails they get, when actually it is the number of actionable emails that really matters. Three confirmation emails equals a 1-3 second scan of each (in the preview pane, not by double-clicking and opening) followed by either a delete or a move to a reference folder. No action, a few seconds used, and moving on to the next thing with no residue.
I love my delete key.
On a related note, this is similar to people sending one long email with some reference, a waiting for, two actions, and a someday/maybe buried inside, all for the sake of not wanting to appear to be sending too much email. I would much rather have five emails, each with a single item, than one email with five. The processing and tracking time decreases dramatically when you can handle them all separately. No re-sifting and re-processing to find the one you want. No worrying that you missed one because you deleted it when you finished the fourth. Give me separate ones, and I can process them all one time.