Using the Butterscotch Pie during the fight against Asgore lowers his attack and defense.
Using the Butterscotch Pie during the Lost Soul fight against Toriel and Asgore helps to return their memories more effectively than ACTing.
If the protagonist causes Toriel to go to her basement without going to sleep beforehand, they are unable to obtain the Butterscotch Pie.
Butterscotch Pie is the only item in the game that always fully heals the protagonist without passive boosts (i.e. Burnt Pan). Dog Salad has the capability to max out the protagonist's health. However, it is not certain at any given time.