For PCs, social skills serves two purposes: a) If the player dump-stats CHA and eschews investing skill points, there is a tangable penalty when interacting with NPCs. b) If the player up-stats CHA and social skills, they are rewarded with additional info, better deals, favorable treatment, etc. It's a payoff benefit for investing in non-combat aptitudes.
A witty player might have a real sharp retort roll off his tongue at the table, but his 8 CHA character with 0 points in Persuasion is still getting a –1 to the die roll. If their quip is especially good, I'd easily give them a circumstance bonus.
The character suffers for thier deficiencies, but the player can still apply personal appeal to the character, in fact having a circumstance reward encourages them. But if they specifically chose for their character to be a social misfit by way of ability scores and skill selection, they should reap what they sow.
Campbell said:
Howandwhy,
Do you honestly believe that the 'silver tongued diplomacy' you engage in around a table with a bunch of other geeks improves your real world social skills or that wilderness survival role playing boot camp makes you any more able to survive alone out in the actual wilderness ?
While there's no corelation between character abilities and player abilites, roleplaying does help improve one's grasp of language and communication. I definitely know that
I've benefitted from roleplaying.
Additionally, the other cascade knowledge skills (mythology, history, math, science) are a nice boon as well.