Blueprints For Old Sand Rails Why Do Some Old Houses Have Blueprints And Such Left In The Walls?

Why do some old houses have blueprints and such left in the walls? - blueprints for old sand rails

I was watching a program called "If These Walls Could Talk" (or so), and the owner of the house he was rebuilding his house they found maps on the walls of his house. I have seen more episodes where other similar results. This standard is more practical? Why do people resort to do? Was this always the case in public buildings or just houses?