Would you keep things from your ex?

I don't know if it's appropriate to post it here but I just want to know your opinions and thoughts. Why do you think your boyfriend/partner keep things (e.g. a letter given by her ex when they were together)  and how would you react to it? 
They broke up a couple of years ago and i've been dating him for 2years. I asked him and he answered that their break up wasn't horrible horrible and they had closure so theirs nothing to worry about