Normally, when you want to check to see if you have any new emails, you have to launch the Mail app and pull down to refresh the email inbox of your choice.
If you're already in the middle of something, stopping what you're doing to check to see if you have any emails is obtrusive. It would be so much better if you could just refresh your email from anywhere without leaving what you are currently doing in another app.
That's exactly what a new free jailbreak tweak called Postman is going to allow you to do, and it works with a key ingredient that most jailbreakers are already familiar with.