Turn On Your Faucets

When it's cold do you do this?  I don't know is this true?  I always thought it was a myth, but I'm not sure.  Do you just let them drip?

My Mom and Dad always tell me to open up the cabinets where the pipes are, but I'm not sure what that does.

Do you let your water drip?  And if you do how long?

Are you worried about a pipe bursting?