When my Sims family members finish their paintings, I hang them on the walls in the "attic" so that when the challenges/opportunities come up to sell or donate paintings I can go there and choose a painting. It saves me time from having to go to their personal inventory and select each painting one at a time to find which one to get rid of and at the same time, to keep the ones that I like. Some of the artwork is really nice and I hang those throughout my house.
I like to use the attic and the lower foundation space to store things - it saves time from having to go to build/buy modes and family inventory - especially if you have a computer that runs a bit slow. Wouldn't it be nice if the family inventory could be accessed without having to switch out of live mode? It sure would save time for me.