There is some advice not to have a smaller pressure cooker because when cooking foods that foam need the extra space to foam. No experience on my part. Any thoughts?
In the same article it said that it takes smaller meals take less time to heat up than bigger meals in the same big pot.
My p-cooker kit came with a 4 qt and a 6 qt. In the literature that came with the set, the only reference to the foaming "issue" is to not fill the pot above a certain level - whichever pot you use. So, the result is you use smaller quantities with the smaller pot.
A 4 qt p-cooker is still quite a pot, quite suitable for many things. But we've mostly used the 6 qt. - pot roast, large salmon steaks, bread, etc. Again, we are cooking for four, so as usual YMMV.
That said, when I cooked my bread, a "normal" one-yeast-packet recipe took two rounds with the 6 qt pot. You'd have to do 3 rounds with the smaller pot if you use a full packet of yeast. Not being a yeast expert (by any stretch), I have no idea if the yeast has any kind of shelf life after the packet is open, so I don't know if you can reduce the recipe to only make a loaf suitable for a 4 qt pot (which would not be much bread anyway).