Belt rank systems, like ranking systems in other areas, were originally created to differentiate between people of different abilities. Over time, other uses/meanings were added: providing intermediate steps that helped break the mass of material into smaller, more manageable chunks, which also aided in consistency/standardization of instruction, providing progress indicators and intermediate goals for students, especially at the lower ranks, where the steps are smaller and faster, and to help people who didn't know each other determine who (probably) knew what when they came together in larger groups.
Like many other organizations that use a rank structure to track progress, the rank structure in many MAs has been subverted to other uses - most notably, and to the dismay of many, the rank inflation seen in many MA organizations. This occurs for many reasons, both good and bad. For me, my rank is simply an expression of my sahbum's faith in my knowledge and abilities, and it is his to bestow or reclaim; my sole interest in rank is that increasing my knowledge and abilities is the only way I can see to repay the time he has spent working on my skills - if he chooses to promote me for having taken advantage of the opportunities he has provided me, that's up to him. Anyone who accepts, receives, applies for, pays for, etc., rank for any other reason is, IMHO, deluding themselves.
