Historical
When clicking on a Building, you may notice a checkbox that says "Historical".
Flagging a Building as Historical simply means that when leveling up the lot, the building won't change. The types of buildings do not have any special effect so this option is purely for aesthetic.
The other reason to flag buildings as historical is if you are doing a quest / task that requires you to have a certain amount of a Building in your City like having 7 pizza places. You should lock every pizza place that pops up.