one nice feature on this phone is auto on/off which does help preserve the battery life. You can set it to turn off overnight (you pick the time) and turn back on in the morning.
to get there go to "options" on main screen and click on "auto on/off"
I would leave it on. When I turn off my Blackberry it doesn't receive calls. I've experimented by calling my phone when it's off - when I turn it back on there is no notification of missed calls, or voice mail. SO ANNOYING.