If your religious affiliation is strong enough to describe you it IS important.
Let's say for example from the day I was born I was a christian, doesn't mean I was a good christian or actually believed in anything. Now my pass says I am an atheist but I do believe in Buddhism.
From that you could only say I am a buddhist, not a christian and not an atheist which, especially true if I made this choice by myself, would tell you a lot about my believes.