Form is a specific way of performing a movement, often a strength training exercise, to avoid injury and maximize benefit.
[1] Exercises or drills in sport have recognized ways of performing movements for two purposes: By using good and proper form, the risk of injury is lowered.
A lack of proper form commonly results in injury or a lack of effect from the exercise being performed Good form ensures that the movement only uses the main muscles, and avoids recruiting secondary muscles.
As a muscle fatigues, the body attempts to compensate by recruiting other muscle groups and transferring force generation to non-fatigued units.
This reduces the benefits in strength or size gain experienced by the muscles as they are not worked to failure.