The difference between the weight used in full squats and the leg press is that the all important lower and upper back is braced firmly when doing leg presses, as is the total upper body. With the leg press, the legs are the only group actually in motion (ballistics)
With the squat, the lower back, and total upper body does not have the benefit of any support/brace at all. The question of balance, shifting of weight and control of the bar on the shoulders becomes that more vital. With squats the whole body (upper and lower) is in motion. In this case the body uses a lot of energy fighting inertia, with less actual strength pushing with the legs/hips & butt. In any case, the lower back can be the key to either the leg press (braced/supported) or squat (non support). The distance of a weight traveled will also have a greater influence on how much weight is used in a exercise. And the benefits obtained..
Some guys who have only done legs press, and never squats, can crack off 2000lbs for reps on the leg press. But might have trouble squatting 400lbs with full squats. Distance and angle of effort also play a role.
Personal view...please do what you think is best for you: If wanting rapid muscle growth and strength , would always include squats (in whatever form) in any serious workout. If a pure BB'er, than throw in lighter squats with leg press as a general pumping up and muscle movement.
Good Luck.