Blowers are really useful for moving leaves, lawn clippings, etc into piles where they can be easily moved into a compost pile or yard waste container. I can understand your confusion if you have never used one, but it is much easier and quicker than sweeping.
IMO where they really excel is getting grass clippings and detritus out of flower beds and off gravel, places where a broom or rake don't work at all. And once you're using a blower for that, you may as well use it for the leaves too.
FWIW I never had much luck with a blower when I was in the north east outside Boston, we had masses of leaves across 2/3 acre in the Fall. I used a rake.
