Sometimes it's a bit difficult to remember to follow up on important emails. You send out an email, forget about it, and hope your recipient replies back with the information you need. A new feature in Gmail now allows you to star or add a label to outgoing emails to help you remember to follow up.
The labels and starring works the exact same way it does in your inbox. Before you hit send, you can assign a label or add a star. The feature works retroactively too, so if you just sent a couple important emails you can go back and star them quickly by browsing your sent folder or clicking the email and adding a label. If you happen to know a person who is always forgetting to reply or you're sending out an important email you don't want to get lost, this is a handy new feature.
Star and label messages before you send them [Official Gmail Blog]