Fitting Rooms are used both as Decorations and a source of XP in the game. You can collect XP from Fitting Rooms by cleaning them when they get dirty. Fitting Rooms get dirty over time. The time it takes for a Fitting Room to get dirty is indicated when you hover over the Fitting Room in your Fashion House.
More expensive Fitting Rooms typically produce more XP and get dirty more slowly.
There are 19 Fitting Rooms to choose from.