When strength training, you need to have proper form and technique to do the exercises properly. For you to lift the maximum weight, your muscles need to be in the ideal position to generate force. When movements become unaligned, muscles are placed at awkward angles decreasing functionality. By maintaining proper form, you will be able to lift heavier and notice visible results in a shorter timeframe.
One of the most important reasons to maintain proper form during weight lifting exercises is to prevent injury. Lifting weight that it too heavy can cause the body to become misaligned and place your tendons, muscles, and joints in positions that can potentially cause strains or tears. A general rule of thumb is to lower the weight if you have to sway your body to lift the weight. It is always better to lift lighter weights with proper form than to lift heavier weights with the wrong form. You can work your way up by keeping your form and increasing the weight slowly. For example, if you are performing bicep curls with dumbbells, and you have to swing your whole body into the exercise to lift the weight, then this is a sign that the weight is too heavy.
Not only can you potentially cause injury to yourself or your clients with improper form, but you will not work the intended muscle group(s). Proper form and technique also ensures correct muscle targeting. This, in turn, helps to ensure you are using proper breathing techniques during your reps and sets. When you use correct form, you will breathe the air in more easily and will be able to focus on the exercise at hand with much greater precision. It is also imperative to correctly warm-up with lighter sets prior to starting your heavier work sets.