Two B's, a B+ and a 2B here.
Mostly they get used for trying out all kinds of cranky software ideas from time to time. For example, how do you download program binaries into a Propeller micro-controller from a Pi?
One has a camera module. It's the best camera I have in the house.
My next project will probably be getting them all running https://resin.io
, just to see how it goes.
None of them has ever made it into part a finished project or permanent installation for any particular function. It's not their fault, that is normal for most of my hobby tinkerings.
Memory in C++ is a leaky abstraction .