Should I be wearing knee supports?

Hi all,
Just a quick question about knee supports.  I'm fine at the moment and havent had any problems but now the weight I am lifting has increased quite a bit should I invest in a pair? I do my big lifts on a smith machine as that all my gym has. 
 
Deadlifts - 140kgs
Squats - 140kgs
 
I play a lot of football\hockey so I want to limit any potential injury.
Please advise.

No.
 
In the interests of your squats, use as much depth as your flexibility will allow. Using proper form will strengthen your knees. Limiting depth can also be problematic.
 
Spooter, I'm not sure if this applies to you, but one of the classic errors made with the squat (Olympic style) is to start the movement with knee flexion, doing this will move the centre mass of the body/bar component forward and this is when the knee is typically exposed to a lot of torque.
 
Instead, initiate the squat movement by hip flexion and sit backwards and down into the hole. As you go below 'parallel' and approach your bottom position, your knees will track a little forward, enabling your back to stay upright and stop you from falling backwards with the weight.