Teens may be in class, out somewhere, or (increasingly) have it locked down by parents during certain times. And they may only get short chances to sneak a look

Teens may be in class, out somewhere, or (increasingly) have it locked down by parents during certain times. And they may only get short chances to sneak a look. Knowing your message got sent (or didn't) lets you mentally set it aside regardless of the other party's status. And if you do sneak a look it doesn't snitch to the other party, like FB Messenger.