I recently started working out and am into a mass and muscle building workout. I do 3-4 sets or 8-10 reps per muscle. The question I have is this; Is it better to lift heavier weight at a "not so perfect" form, or is it better to lift lighter weights in order to keep the form correct? The way I see it, if you're lifting heavier weight then you might be cheating by using other muscles but, nonetheless, muscles are being used...

What do you think?

To cheat, or not to cheat. That is the question! It's actually a great question, because you had the awareness about exercise technique to ask it in the first place! Most people aren't even aware that they alter their technique (cheat) on everything they do thereby sacrificing proper muscular development and safety. The main reason people cheat on their exercise technique is that it allows them to use more weight or to complete a set of repetitions when fatigue starts setting in. But, cheating goes much deeper than this in the rhealms of training lore. :-) Let me explain.

There are three main categories of cheating:

Category 1 Green Cheating
This type of cheating is usually used by somebody that is just starting out with a training program, hence the term "green". I mentioned this above and it's simply when a person does not know the proper technique in the first place. There are no ulterior motives to their cheating. They don't have an ego problem and are not trying to use more weight than they should. They are not using a specific "overloading" technique to stimulate additional muscle growth. They just don't know. This problem is easily fixed with proper instruction or by studying the exercise definition and video library at Fitrex.com. Here are some common mistakes beginners make:
Improper Breathing
Maintaining Poor Posture
Limiting Range of Motion
Training Too Quickly

Category 2 Ego Cheating
This type of cheating is probably the worst because it causes injuries This person knows how to do things correctly but they don't because they just can't stand the thought of using less weight on an exercise. Doing things correctly and being able to isolate a muscle group takes more work. So, they continue to "throw" weights around and never seem to make any progress. Here are some common things "Ego" Cheaters do:
Arch their backs off the bench during a bench press
Throw a weight up with their legs and back when performing bicep curls
Bounce weight off a weight stack creating momentum to lift heavier weights
Use short, jerky movements to complete the reps on a set

Category 3 Advanced Cheating
These type of people cheat for a physiological reason. There is actually something called a "Cheating Principle". A phrase that was coined by the great Joe Weider. Notice that I didn't say developed. It's actually been used by people forever he just put a name on it to sell a book or something! Anyway. There are times in a training program, if you reach a certain level, that you would want to overload a muscle at a particular joint angle or during a particular movement. Eccentric loading, for example, is a term that describes emphasizing the down phase of a lift such as lowering the barbell during a bicep curl. But, in order to lower the weight you first have to lift the weight. This is where it gets tricky. The advanced cheater would first use a weight that he or she could curl with perfect technique for 6 to 10 reps. Then, they would use their legs and with a certain rhythm be able to "pop" the weight up. Once the weight was up they would slowly lower the weight for 4-5 seconds back down to the starting position. On the other hand, the ego cheater would start their training program like this and never do a perfect rep! Now, this type of training is not for everybody. You actually have to learn the proper technique of cheating so you don't kill yourself in the process! For most of us however, it is probably best to stick with the fundamentals. You can never go wrong if you learn how to train correctly and you stick with it!