It's kind of annoying when you send a message only to have it lost because you didn't click the "Save in Sent Items" and no one replied. What do you think?

Not really. You do realize that the Admins never set the PM Inbox limit of messages other than 50 default. I know that for a fact here.

Plus, it wastes up space if you haven't noticed. The Admins CAN set it so that members' Inbox message limit higher than 50 messages. *shruggs*

It's really up to them, IMO.

Though, why you would want to save your Sent PMs is beyond me.

You might want to save your sent PM's to see if you've already sent a message to somebody, or to review the contents of one. It is a quite useful feature, that I agree should be standard.

like an outbox