Why in the world would you use the Gmail app on your phone to send or request money? Because now your can. That's what the Gmail app on Android lets you do thanks to an update that is rolling out to U.S. based users only. According to Google, "sending money in Gmail is as easy as sending any other attachment. Just tap on the attachment icon and choose whether you want to send or request money".
The recipients do not need to install a payment app on their devices and handle the transaction right in the email itself. This whole activity of sending or requesting money is free for all parties involved.
If you live in the U.S. check out the update in Google Play Store and use Gmail to send and receive money.