One of the most popular exercise machines in most gyms is the Leg Press. Many guys incorrectly use it to gauge their leg strength. It can be quite easy to throw 100 kg or more on the slider to impress people. Unfortunately, you are not actually lifting the weight with your legs, the slider does most of the work.
Some experts suggest that a person may only be lifting 50% of the weight. A good feat if, lets say, you are lifting 300 kg which means you are only lifting 150 kg. To test this, take what you normally Squat at 1RM and see if you can double that on the leg press. You should be able to Squat 50% of what you leg press in theory.
I keep the leg press in my workout since I feel it helps compliment my back and front squats.