You should always be striving to achieve range of motion standards. The only exceptions are flexibility limitations. Often it is hard to tell exactly where you are in a squat. Developing that "body awareness" takes some time. If an bbject, such as a medicine ball or plyo box helps you, go ahead and use it.
If you are ever competing a judge will be watching you to make sure you are hitting the required ROM standards. Don't miss repetitions. Each one you miss is wasted precious energy.