A Blue Chair, facing south.
A Red Chair, facing south.
A Chair is an Obstacle that can be found inside Hideouts.
Chairs come in two varieties: Red 
or Blue 
. For all intents and purposes, both types of Chairs are exactly the same as far as gameplay is concerned. Chairs may be oriented in any direction, and are never found adjacent to a wall.
Chairs are some of the most common types of Furniture in the game. Both types often appear in Offices and Lounges. Blue Chairs tend to appear in Computer Rooms, while Red Chairs are pretty much the stable of Storage Rooms and Cafeterias.
Chairs serve absolutely no purpose - they cannot be Photographed nor Bugged.
You can hide behind a Chair when crouched, and can also jump over it if necessary.
The Chair at the Center[]
If there is an Agent Room inside any building or Hideout, it always has a Chair near the center, facing south. If the Agent is present (I.E. hasn't been grabbed by Max for an Arrest), the agent will be sitting in that chair.
Also, if Max is ever Captured by enemy agents during a Break-In, and decides to try to escape his captors, he will appear on top of a chair in one of the rooms (the same chair the Agent would be in, if this hideout is the residence of an agent). The moment Max moves from this chair, the alarm will immediately go off.