[1] It requires an invitational hand with at least 10 points, or 12-13 upwards if it is game-forcing and opener has not shown any extra strength.
The convention was introduced by the British bridge author Norman Squire and is adopted by the majority of partnerships playing at competitive levels.
Opener will generally pass a rebid in responder's second suit, knowing the hand opposite is very shapely and weak.
With ill-fitting hands, lacking game going values, a bid in the fourth suit will often allow the partnership to subside in a playable contract in a reasonable fit, at the two-level.
However, he does not have a good natural bid available; each would give partner the impression of stronger support than he has, and might lead to a poor choice of contract.
The fourth suit forcing approach in conjunction with the principle of fast arrival allows the partnership to create a game-forcing auction at low level that leaves ample room to explore for slam.