Don't get me wrong, if you have a good jam or preserves it's totally fine on a sandwich, and I wouldn't turn my nose up at it. However, peanut butter doesn't really need the help, and the extra sweetness from jelly is totally unnecessary. Toasted bread and peanut butter is all you need for a quality simple sandwich.
Umm… I am unsure how to proceed. Out of pure curiosity, I want to try a peanut butter and pickle sandwich. However, the portion of my mind that is closed does not want to try that.