The battery thing is a grey area. I don't think anyone should tout push mail as a boon to battery life.
But plain and simple, push mail gets your new e-mails to your phone faster than if you check on a schedule. Say you've got two Pocket PCs set up to check your exchange account. One is set up with POP3 on a schedule to check every ten minutes. The other is set up for direct push.
So the one phone on a schedule checks for mail at 3:00pm and finds nothing. Ten seconds later a new urgent e-mail comes in from your boss/wife/bookie. The phone with push enabled will get that message by 3:01pm (most likely sooner), while the the other phone won't get it until 3:10pm when it does its next scheduled check. Those ten minutes might be what saves your job/marriage/life!
Heh. Well, 90% of the time it means you get your spam and buddy's joke forwards a little faster, but you never know when that crucial e-mail will come!
But for many of us, I think the allure in push is that it provides very seamless synchronization, not only of e-mail but also of contacts, calendar items, and to-do lists. To me anyway, that is the holy grail of convergence. I absolutely hate having to enter data twice or maintain two separate copies of things. For instance, POP3 e-mail accounts are the bane of my existence because you can't use multiple computers/devices to maintain that account without duplicating all of your replies, deletion, and organization. IMAP helps in that regard, but it's still nowhere near as smooth as exchange is.
Ideally you want to enter data once and then have changes to that data reflected as soon as possible on all devices that you use to access it. So in that way, Exchange push gets your data synced faster and more seamlessly than any other method.
And that's why you should want push as opposed to scheduled mail downloads, despite the battery hit.
