Well, because this allows agents, managers and casting directors a way to keep an eye on emerging talent all from the comfort of their desk or home computer...in 10 minutes or less. Here's another thing they'll like.  They'll know you're serious about being an actor (you don't know how many of them complain that even their own clients don't have demo reels--or have outdated reels) and they'll know what you look like on tape, what "types" you can play...and, of course, you have a SpeedReel which is something they appreciate as it makes their life easier.

Oh, wait, you mean why should YOU do it? Well, because unless you're turning away offers for good representation, love spending hours putting together mailings, and can't get enough of spending hundreds of dollars on showcases that don't pan out then what do you have to lose?