With a slot punch, you'll be able to poke neat holes in your ID badges through which you may thread a lanyard or neck chain. This way, your staff, students or convention guests can wear their photo IDs, making them easily visible to your security personnel.
Depending on the volume of cards you'll need, you may decide that an electric slot punch will be more convenient, but handheld slot punches also work well for making small batches of wearable ID cards.