1.

The ability to restrict opponents from immediately taking tricks in a their long suit, particularly when bidding Slam.  Aces are considered first rounds of control, with Kings counted as a second round of control.  In situations such as cuebidding controls after trump is identified, voids may be counted as first round controls and Kings second round controls.  Also see Italian Cuebidding

Cuebidding Controls, Part 1 - Slam Bidding

2.

The Ace-King control count system enjoys popularity in various conventions:
 

Ace	2 controls
King	1 control

3.

Another control point count system uses steps:
 

First	0-3 points
Second	4-6 points
Third	7-9 points
Fourth	10-12 points

4.

Yet another control system counts each Ace or King as a control with step responses:
 

First	0-1 control
Second	2 controls
Third	3 controls: Ace & King
Fourth	3 controls: 3 Kings
Fifth	4 controls
Sixth	5, etc...

5.

Advanced methods associated with the Precision system make use of several control-showing bidding structures.  See Alpha Cuebid , Beta Cuebid, Trump Asking Bid, Control Asking Bid, Suit Asking Bid, Delta Asking Bid