Well, first there are only a few media that can be burned at that high speeds.
Second you will gain a few seconds, since the drive at the beginning will start spinning at higher rpm, but in the end it will drop at a slower speed (at least thats what my LG does).
So it all ends on what you need, if you need speed try to find an e-sata (thats if your PC has an e-sata port) other wise you will have to leave with a slower speed (not a big loss).
BTW, my lg had some kind of USB speed booster software. and with that it could do 20x (sometimes no problem with 18x) but that software only worked on 32bit OS plus i didn't need all that speed.