1. entry through a long hallway--cs may be used to prevent tangos from entering the far end of the hall and opening up on your team while they are vulnerable in the hall.
2. stealth entry into a large room with lots of cover--cs thrown into a key area where tangos may be waiting in ambush will flush them out to a position where you have the advantage.
3. dynamic entry into an L-shaped room --cs gas deployed to a deep corner just prior to a short flashbang giving the team a few seconds to clear the front before proceeding to the back.
4. to the bottom of a stairwell--cs can flush a tango out of his position of advantage preventing him from shooting at your legs before you have eyes on him.
5. as a barrier to temporarily deny tangos access to an area that can not be permanently barricaded.

In general using CS as a room clearing device, while effective in the game, would not be viable because visibility would be poor, making it difficult to place shots. Also, we don't use masks very often, so placement is crucial. Sometimes tangos have masks and we may not detect them in a hidden areas. They have a tactical advantage in that situation since AI can't see smoke.