This is going to be specific to a low bar squat

There are typically 2 sides of the debate regarding the knees during squats

1. Knees shouldn’t go over the toes because it’ll stress them too much
2. Knees should go over the toes because keeping them back will make your technique disgusting
   Or something along those lines
   These points seem to be on the two ends of the extreme, and I prefer something in the middle
3. Let the knees travel forward as much as they need to at the start of the movement, however, avoid them going excessively forward more than required.

Providing a visual for point 3 using Aimee above. On the left video, her knees drift forward too much at the bottom of the movement which is causing a few inefficiencies:

1. Her weight is shifting into her toes
2. The bar has too much horizontal travel and is going toward her toes. This opposed to remaining in a relatively straight line over the middle of her feet
3. Squatting too much into her knees tends to cause her hips to shoot back and chest falling forward as she comes back up

On the right side, we are focusing on letting her knees initially travel forward as much as they naturally need to during the top 1/3 of the squat, but then, not letting them drift any further forward for the remaining 2/3 of the movement.

By doing this (right video) her weight is keeping more in the middle of her feet instead of shifting to her toes, the bar is remaining in a straighter line over the middle of her feet, her hips aren’t shooting back nor is her chest falling forward as much. The right side is not perfect, she goes slightly into her knees too much on reps 3 to 5, however, her squat looks more efficient relative to last week.

Back to the two debates at the top of this post, the knees can travel forward over the toes if they need to depending on the measurements of the person, however, we should still have some control of keeping them back. People with longer legs may need the knees to go over the toes by some amount, but people with shorter legs can probably keep the knees behind or in-line with their toes.