Charming is a when you flip a unit or commander's allegiance to your nation. It is distinct from Enslavement in that, if you charm a commander, they remain a commander after the fact. This has many advantages; magic skills are readily used, magic items and gems aren't dropped, and the fellow can understand the vague directions that are your five-turn scripts.
Methods of Charming:
Seduction and Soul Transaction are geared around keeping the targets, while keeping anyone charmed by the others can be somewhat difficult. Seduction avoids a battle entirely if it succeeds. Soul Transaction, on the other hand, has the target rout and makes them Invisible if it works. There's an additional impediment to Soul Transaction, in that the Penetration roll must also go against the target's Morale. For other spells that charm targets, the charmed target continues to fight, which can very well get them killed.
Charming is always somewhat risky for the charmer, due to the intimate nature of Seduction and the mostly-short range of the spells. It's also difficult to get a specific target charmed, due to the randomness involved in targeting.