As a point of snark, I feel that some role-playing games thrive on roll-playing.  That's fine and dandy within the spirit whence the table at play perceives the word, fun.  But there are times where dangling plot threads and character motivations are greater than some chunky modifiers on die rolls.  Because of the theater which goes on routinely at the table, one should look at how exactly wants to adjudicate the game.
Some characters might upset the balance of your table.  Some characters might be well within the defined rules, but with no context, just be out from left field.  There must be a reason, and explanation, as to why such a plethora of talent would be within one single entity...
and I present you referee's of table top RPG's...
Due to how The Game is, you can see that an 18 in an ability score is subject to be excited, and should the character be able to have modifiers, they would be the type of person who would be known as a pinnacle of that attribute for that race. Excited referees should make their players write an essay describing just how it is to be heralded by members of the community for being able to have such a blessed and natural ability to have such an ability score.