Charm is particularly weak in 5E (compared with older editions), which is why I've removed the "automatic knowledge" of the charm from most effects (it's an Intelligence/Arcana check instead). In combat, this generally means that you won't be attacked... and nothing else. I've allowed for a Persuasion check (DC: 10) as an Action to convince the charmed target not to attack your friends. If one of their allies tries to convince them to continue attacking, it becomes a contested roll. You can convince someone to attack their allies, but only if there would be a reason why they already would. For example, a succubus charmed the barbarian in our game, and convinced him to attack the party's elf... because she convinced him he was the one that had stolen his magic sword (actually by the rogue under orders of the sorcerer, but that's a long story).
