I've got several dutch ovens, and I don't designate any single one for any particular type of dish. I use them all (big to small....) for everything, generally depending on the situation and/or portions desired.
Now that I think of it though, I DO generally give a little sniff test prior to cooking a cake/cobbler in one, just to make sure the smell from the onions and/or peppers from the previous meal is not still lingering... ;-)
I use several iron pieces, and the one segregation I observe is there is only one skillet dedicated to fishing camp/fish fry duty. Otherwise, I run anything through all the rest.