Control Wards Disable ememy wards that are in their 600 range area of effect.

When you are taking an objective such as a drake, Rift Herald, or Baron Nashor drop down a control ward to reveal and disable enemy wards.

Pro-Tip 1:

DO NOT attack the enemy wards that are revealed by your control ward as this will give the enemy team vision of the champion attacking the enemy ward.

Control Wards also reveal stealthed traps such as Teemo's Noxious Trap, Jhin's Lotus Trap from Captive Audience, Nidalee's Bushwhack traps, and Shaco's Jack In The Box.

Control Wards used to disable the traps but that was removed in Patch 7.4.

Pro-Tip 2: use attack move to kill off the traps so you don't accidentally path over them and set them off.

In the case of Shaco's Jack In The Box you'll want a ranged champion to use attack move to kill it so you don't get within its activation range.

Control Wards will also reveal camouflaged units so that you can target them, but it will only outline invisible units to give you an idea of their current position (you won't be able to target them with basic attacks or point and click spells, however you can still hit them with skill shots which will make them shimmer briefly which might allow you to throw something even nastier their way).

It gets a bit confusing on who has camouflage and who has invisibility so if you are having trouble with a particular champion do some research and see what kind of stealth mechanic they use to figure out options for dealing with them.