Character Traits when do they belong?

I read a tweet by an agent which advised not to make a character have a trait without a need for it.  So my question is when do you think it is needed?

Anna and the French Kiss by Stephanie Perkins always has St. Clair biting on his pinky finger.  She describes this so well I can actually see him biting it.  It is not over used in my opinion because he bites on it when he is nervous or thinking.

Colin Bridgerton by Julia Quinn is always eating.  His family and friends know to ring for food anytime he visits.  I've seen alot of characters both on television and in books that love to eat food.  Like the Gilmore Girls and their coffee habit.

Do any of your characters have habits/traits and how do you know they are needed?

Status on my 2011 resolutions

Some of them are not going so well.  My writing progress thankfully is not one of them.  I have joined NJ Romance Writers Chapter.  If you live in New Jersey and like to write come to a meeting.  They are extremely friendly and welcoming.  Which for someone as shy as me, it is appreciated.

The meeting made me realize I have not submitted to an agency since October.  I plan on correcting that this weekend.  As well as register for RWA National's conference on the 18th.

I'm new a blogging, but as soon as I learn more I'd love to have people come and visit me here.