When I was growing up, we didn't have guests over very often. Occasionally we might have one or two people to dinner, but the only time we really had a houseful of guests was at Thanksgiving, when my dad's whole side of the family (his mom, his two brothers, and later, their spouses and my cousin) would come for the whole weekend. At those times, my mom would often say that she wished her house were expandable. Our modest 3-bedroom, 1.5-bath house was plenty of room for just the four of us, but it wasn't enough to hold the whole family comfortably. And nowadays, the problem is even more extreme; the house is more than big enough for the two of them since my sister and I moved out, but the Thanksgiving guest list has now grown to four couples plus two kids. Mom definitely doesn't need or want a bigger house on an everyday basis; having more rooms would just invite more stuff to fill them up. But it would sure come in handy to have a few extra rooms that could be folded up and stored most of the time, where they wouldn't have to be cleaned or heated and cooled, and then set up just for that one weekend.
What struck me about this the last time she mentioned it is that, in essence, an expandable house is exactly what Brian and I have now. We have the rooms we use every day––the living room, the office, the bedroom, the kitchen––and then we have the whole downstairs as, essentially, that extra expansion that we can set up when we have guests. Moreover, it doesn't have just one function; it has been, at various times, a guest bedroom (with its own bath), a board-game parlor, and a music room. (No wonder we had so much trouble coming up with a name for it.) And since it's not in use most of the time, at other times it doesn't need to be cleaned (beyond a quick sweeping or wipe with a rag) or heated in the winter. The very fact that it's not used every day, but only as needed, makes it actually one of the most useful rooms in the whole house.
Thinking about our extra room in these terms makes me feel better about our decision to turn our small room into an additional guest room. I settled on that use for it because I couldn't think a better one, but part of me still felt like I really ought to try to turn the room into some kind of space we would use every day, rather than a guest room that will almost never be used at all. But when I think of our house as expandable, containing the rooms we live in plus the extra rooms we use for guests, then it becomes obvious that by making this room a guest room, we're simply adding it to the expandable part of the house rather than the everyday part. And since we already have all the space we need for our everyday activities, adding this extra room to the expandable section is clearly the best use for it.
Moreover, even after it becomes part of the expansion, this room can still do double duty for all the everyday functions it has now: starting seedlings in the spring, storing cookbooks and pet supplies, sorting our recycling, and wrapping gifts before the holidays. It won't just be changing from one type of room to another; it'll actually be several rooms in one. In fact, maybe we can refer to it by different names––the guest room, the conservatory, the lumber room, or even the recycling room––depending on what we're doing in it at the time.