Some clearomizers have replaceable heads. This is for economy. Your atomizers have a life span, and the working part that has the shortest longevity is the atomizer coil (a coil of metal that is heated every time you draw on your e-cig). Because this does most of the work, it goes first - the rest of the clearomizer can still be in perfect condition. Therefore, rather than throw the whole unit away some people prefer to buy clearomizers with replaceable wick/atomizer heads. Keep in mind that if you look after your clearomizer and do not over-vape (keep puffing when it gets very hot , or labour it too hard) it will last a reasonable length of time. Think about it like a car: if you race around and always have your foot on the accelerator, your car would have a shorter life span too.