Much like equipping Gear, equipping Furniture will boost your overall stats using the individual stats of the equipped pieces of Furniture.
The number of pieces of Furniture you can equip is limited, but will increase as you raise the Rank of your Room.
[How Stats Are Shown]
Stats shown on the below screens are as follows:
-Gear Equip and Gear Set Screens
The total stats of Gear equipped

-Room Menu and Furniture Equip Screens
The total stats of Furniture equipped

-Player Profile Screen
The total of stats of Gear and Furniture equipped