Previously, when a person brought a check or cash to the church to pay for an event that was actually an online registration, you created a coupon and had them use that code on the payment page instead of making their payment online.
Also, there were times when a person paid their deposit online, but wanted to make subsequent payments using a check or cash. In those case, you also had to create a coupon and have them use that with their paylink.
There were even scenarios in which the fee actually changed after someone had already registered online, and you needed to adjust the balance they owed.
All of those scenarios and more are now handled using the new Transaction button on the person’s Member Dialog. I will not go so far as to say that you will never need coupons again, but it will greatly reduce the need for them. Also, it makes the process much easier for both you and your registrant.
You will want to read all about it, in order to understand everything you can do with this little green button.