Control wards are for more than just being a permanent ward, they are vision control which is one of the most important aspects of the game. Throw one in Baron and the enemy team can never so much as go near it without you knowing. Throw them in river bushes and make sure the way is clear for your jgler without losing your ability to place normal wards. They can also become points of contest. If you are ahead in lane you can throw down a ward in the bush and force your enemy to not have vision. Any time they want to clear it they have to worry that your jgler is waiting there for them.
Also be aware that as you rise up your laners will learn to not give themselves away. They will walk up to last hit a caster minion then blow their summoners on you as Lee hops in from tribush behind you.
Control wards also let you spot out junglers which grants a huge amount of power to your team for a short time if you have them in river bushes where laners are unlikely to wander by and clear them out.