yelling at your kids

As I was in a waiting room this week I noticed how one mom got her son to “behave”. She was yelling at him. This boy was 2 and not being very unruly, just acting like a toddler. She had an infant with her as well and I feel she was maybe a bit overwhelmed. As she procedded to scream at him to get him to comply ( it didn’t work, only made him act out more) I had to wonder if this was the techinique maybe her parents used on her. Is this a common parenting practice? Should I have offered to help her? Do you ever yell at your kids to get them to behave?