The biggest problem with jailed prisoners is their being starved or dehydrated to death because the job scheduling for feeding and watering prisoners is frankly buggy. So having a food and/or drink stockpile within range of prisoners does tend to keep 'em alive. As for other beards having a snack using those stockpiles, I don't worry about it. The reason is that I have the prison stockpiles linked to 't'ake from the primary food stockpiles in the fortress. The job to transfer a barrel from the primary stockpile to the prison stockpile seems to have a fairly high priority and any food taken from the prison stockpile gets rapidly replaced with something fresher from the main fortress stockpile. Additionally, I have every prison chain within reach of a well so if worse comes to worse, the prisoners can always drink. Here's my prison cell layout.
####### # = Wall
#BFDFB# B = Bed
#FcDcF# c = Chain
#CTWTC# C = Chair
#FcDcF# T = Table
#BFDFB# W = Well
###.### F = Prepared meal stockpile
D = Drink stockpile
Every prisoner has shared access to a table and chair in which to eat meals in a "proper" environment preventing bad thoughts in that direction.
Additionally, each prisoner has exclusive access to 2 meal stockpile tiles so they don't starve to death. They also have shared access to 2 drink stockpile tiles so they usually get to drink booze instead of water. But if worse comes to worse, they have access to the well so they don't dehydrate. Finally they have exclusive access to a bed that's out of reach of the other 3 potential prisoners in the room so if one of the other 3 happen to be a vampire, they don't get drained while sleeping due to being a cellmate with a vampire. Very rarely will a prisoner go hungry or thirsty with this arrangement since the food and drink stockpiles 't'ake from the main stockpiles in the fortress and as mentioned earlier that job seems to have a fairly high priority. I will admit that non-prisoner beards do stop by from time to time in order to have a meal or drink, but that just simply causes the stock to be replenished.