autofocus - What is AF-L needed for?

After quite a lot of reading even, I am not being able to grasp the rationale behind the AF-L part of AE-L/AF-L button on Nikon D5300. If the camera is set to AF-C, then the concept of locking focus at a particular object/distance makes no sense. Hence, I am assuming AF-L is relevant only in case of AF-S. However, I can keep auto-focus locked by simply keeping the shutter half-pressed. Nikon doesn't provide an AF Lock (Hold) mode. Essentially, it means that the focus will remain locked until the AE-L/AF-L button is kept pressed. What is the preventing the photographer from keeping the shutter button half-pressed and then recompose rather than having a dedicated button with a fancy feature? Isn't it a redundant functionality assigned to a button which could be better used for some other purpose? Am I missing something?