i have lot of them and i like to spend it on BG accessories however the npc where you can exchange them requires you to be the same job that is applicable to the desired accessory to be exchanged (ex. if my job is acolyte class i can't exchange my bg badges to swordsman badge)
also i think BG badges (including KVM items) should be storage-able and it would be a waste if i can just keep all of my badges without spending it