[From the “at least once asked questions” series, I was recently asked if it’s less expensive to hire a guy to blow all the leaves once they’re all down, rather than as they fall]
Leaves fall in the fall, but they don’t all fall at once. As anyone who rakes their own leaves can tell you, it’s a lot easier on a body to rake them once a week or two rather than waiting for them all to come down and then rake them. The same applies if you’re using a leaf blower.
Leaves piled on top of leaves are just harder to rake or blow. Leaves on top of wet leaves are a nightmare no matter what you’re using to move them. Wet leaves on top of wet leaves are, well, worse (and also a good way to kill a lawn or garden).
Gathering your leaves as they fall is the best for your lawn, gardens, and whomever it is who is gathering them.