Complete oil system cleaning service

My daughter takes her car to the local repair/tire shop for oil changes and occasional service. They are now regularly recommending a “complete oil system cleaning service” to the tune of $50 in addition to her $50 oil change (synthetic oil). Is anyone familiar with this service and is it legit? I thought that was the purpose of the oil change. Any enlightenment would be appreciated. Personally, I think it’s a scam unless others can convince me otherwise – especially with synthetic oil. Thanks.