Exploring the play – emergent and otherwise – of OD&D we have noticed recently that charm person in OD&D is a much more powerful spell in OD&D than in later versions of the game. In OD&D the victim comes
completely under the influence of the Magic-User until such a time as the “charm” is dispelled (Dispell Magic).
Without periodic opportunities to shrug off the charm, the Magic-User casting charm will accumulate a growing mob of completely loyal followers. In charming the occasional orc or goblin there is natural attrition as these allies-of-convenience set off traps and act as meat shields. But what is to prevent even a low level Magic-User from slowly charming everyone around them and building an empire, one magically loyal servant at a time? A few things to consider:
First, in a world where charm person exists and even the least accomplished of Magic-Users can cast it, this will be a common danger. Those able to cast dispell magic will do so on themselves and their retainers frequently. Established authorities, heroes, and higher level Wizards will seek to slay or co-opt Magic-Users indulging in this pasttime too often, and having a reputation for casting charm person will quickly become a liability in dealing with others.
Second, this permanent charm is easy to take for granted. But a dispell magic can instantly turn a faithful bodyguard into a savagely vengeful enemy, who has had months or years stolen from their life.
Third, especially for player characters, charm person is not very efficient when used on what would normally be a hireling or retainer. No matter how well you treat them or how long they serve you, thier loyalty will always be subject to dispell magic. Like a mid-tier chess player, the magic-user who uses charm too often will eventually box themselves in, surrounded by a charmed retinue, unable to attract or recruit other allies. In the long run, better to simply treat your retainers well, and earn their true allegiance.
(This does not apply, of course, to evil Magic-Users who charm everyone and treat them horribly… but they are generally the bad guys the PC’s are trying to kill, which reinforces the point).