In harry potter, the actors were chosen at age ~8 (ish, young what ever it was)
This meant that in the middle movies, they went through puberty. My generation of VFX people cut their teeth doing puberty based acne removal. Both harry and ron had pretty bad zits, and because continuity is kind, the needed to be removed.
Meryl Streep in MamaMia had "digital makeup" applied by one bloke working the night shift.
TIL