Concise answer
Squeezing can push inflammation deeper, tear surrounding tissue and increase the chance of dark marks or scars. Deep acne can scar even without picking, so prevention also requires controlling active disease.
Repeated pressure is especially risky when a lesion is tender, deep or has no clear surface opening.
Post-acne colour change is different from a permanent indentation, but both can become more noticeable after trauma.
When evaluation may help
Seek early acne care when lesions are deep, painful or leaving marks, rather than waiting until new scars have accumulated.