Cat collars, leads, and harnesses come in many styles and purposes. Practical or decorative what do you need a collar on your cat for? Depending on your location a collar with registration is a requirement to cat ownership.
Collars can prevent fleas and ticks. Give your feline friend a sense of style with a colourful or blinged up collar. Add kitty's details to a tag on the collar so they can be easily identified if the wander far from home. Colour co-ordinate a collar with a harness and lead to teach kitty to walk with you.
A very good idea is a little bell to warn wildlife of your cats approach for any outdoor cat. If your cat is an indoor only cat then you may find a collar irrelevant so consider the pros and cons of putting a collar on your pet.