Yes it does affect your rank. Without merit points you will not get a rank above jr. member. By getting merit points you're getting the ability to give points to other posters and with rank gain the ability to have an avatar and visible signature under your profile. If you don't care about these things you can ignore merit, but keep in mind that it also works as a proof  that your posts are being noticed by other people and that they want to award you with points. If weeks go by and you can't get a single point it says something about your style of posting.