depends. I buy peanut butter pretty regularly. So when one jar starts to get to the point where Id need a spatula, I open a new one. My cabinet is filled with almost empty jars, but with enough left to make it reasonable to one day use.
toothpaste is bought like once a month, and buying more means leaving the house, driving, parking, browsing, waiting in line, paying, leaving a parking lot, driving, parking, then opening the toothpaste. I will use every last bit of that mother fucker. That is too much effort to buy a new one.
EDIT: yes i realize that you have to do the same for peanut butter, but I buy it like twice a month with the groceries, Im already out of the house. Toothpaste just kinda gets foirgotten