I normally have no use for social game mechanics in role-playing games (as my favorite activity in such games is role-playing), and ordinarily I ignore those character skills that are used to replace actual social interaction with skill rolls. I find it far more enjoyable to haggle in character than to roll a character's "Bargain" skill, far more challenging to attempt to be persuasive than roll a "Persuade" skill, and far more interesting to ask questions than roll an "Interrogate" skill.
Sometimes, however, rolling dice isn't anathema to the role-playing experience. Take the original Ghostbusters role-playing game. Don't take mine — get your own! Characters in Ghostbusters have four Traits (Brains, Muscles, Moves, and Cool), and one Talent for each Trait. Players and Ghostmasters may define Talents as they choose, or they can select from a list of examples. Many of the examples are social in nature and require one to roll against an opposing Trait or Talent. A Ghostmaster could rule that social Talents are not available, but a great opportunity would be missed: the opportunity for comedy. Ghostbusters is, after all, a game of humor first and foremost.
"How can saying 'I use my Seduction Talent' be an opportunity for comedy?" you might ask. Well, that's not all you say. You role-play it in addition to rolling for it. If the Ghostmaster decides that you were convincing, you are awarded bonus dice in proportion to your performance. If not, well, you roll normally. Regardless of whether you succeed or fail, there's always the chance you'll roll a Ghost, which generally means slapstick happens.
So, the answer to the riddle is "choose both." At least, choose both in those games where it can be beneficial to the gaming experience. You might find this could work in your Call of Cthulhu game, where a good performance could garner the player a skill bonus of +10% (or whatever seems appropriate). In a Fudge game with social skills, impressive role-playing might increase a skill by one or two levels. Regardless of the game system, the GM should feel free to call for any method that he or she determines is best at the moment. For instance, a GM might prefer to require role-playing at all times, but only call for a skill roll when he or she is undecided about a non-player character's reaction. In such cases, a social skill is an edge instead of a crutch. In Ghostbusters, though, choosing both is always best. It leads to more tomfoolery, which is never bad. Unless it is.
