The whole point of firecrackers, IMO, is that they are so quick and easy to make. If you are going to complicate them, you may as well make cookies are something.
Why would adding butter to peanut butter make them any more potent?
Because it increases the total fat content %.
If you aren't using too much weed, then the peanutbutter (which is around 50% fat) isnt TOO saturated with THC, so you don't have to add butter.
If however, you are using lower quality weed or have a very high tolerance, adding oil/butter (oil is better because its 100% fat, butter is like 88%) will allow you to add more weed without over-saturating the peanutbutter.
So its a situational thing, don't always need to add oils to it.