PB sammiches are best used for gaining. for hardgainers who just cannot seem to get enough calories down. PB is a very calorie dense food and as sleazy said, if you use the natty stuff you are getting healthy fats. its a great, calorie dense food to help you gain when stomach is always at capacity.

if you are trying to lose, or put on fat easily then it probably be wise to avoid PB sandwhiches