A lot of those items you list as used only once in a blueprint make sense to me – many are decoration items, and the fine tall window is pretty new.
When I’m designing custom templates, I usually leave the decorating for later, once the building is complete. If it’s a late-game house I might add all the trimmings to the blueprint; but most of my building designs are supposed to be flexible.
I learned that the hard way with my “wizardly tower” template (I haven’t uploaded any templates anywhere, but think of a very stereotypical round-ish tower with a pointy roof and a room on the side) – it’s an Ascendancy-styled building, but it has everything from clay windows to fine comfy beds, an Herbalist’s workshop, potions on the windowsill, and even a pottery workshop. When I originally built and decorated it, my potter and herbalist had the same last name so I set this tower up as a “family home”, where each went about their separate careers.
Skip ahead to my next game, and I go to build the tower… oh yeah, it’s full of late-game products, and I don’t even have a potter yet. I tried going in and manually deleting all of the items I couldn’t build at the time, but it turns out that squeezing them in there was a lot easier than getting them back out again lol.
That experience taught me that it’s easier to save a template before it’s decorated. After all, if I want a decorated copy I can easily make one later. I suspect that a lot of other players have hit upon the same idea; particularly any who create templates regularly.
I usually end up adding more furniture to my buildings over time, and by the time I’m building “advanced” fully-decorated templates my starting buildings will be fully decked out. It’s just the easiest way to do things at the moment – create the building first, and add cool stuff to it as said cool stuff becomes available.
With all of that said though, this is still a very useful insight – both for casual players, building whizzes, and the Devs too. Thanks for sharing your findings