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.
And cheddar cheese and strawberry jam sandwich is better than just the cheese sandwich by itself. I learned this years too late.