Really.. it is quicker for you to shutdown your Mac than it is to put it to sleep?
Thats right, as explained above it can be safer to shutdown and there is no waiting around for the hard disk to spin down (although some people may not wait for that).
However..having said that, I will wait for it to sleep 9 times of out 10 as I like everything to be as I left it, and its quicker to wake from sleep than to start it up. I would use shutdown when Im packing it up for long journey if Im afk for a while.