Belt slot vs backpack: potions

Martin,

Thanks for answering items here. It's great to get a definitive answer for us.

My question is regarding belt slots vs. backpack space. I do not see the advantage of putting potions in the belt slots since they can get damaged when attacked in the belt. In order to use a potion, either in the belt slot or in the backpack, both require that one not use an attack action in order to use the potion...

So what is the advantage of having things in the belt slots outside of having extra space once you run out of room in the backpack?