Often, an instance of a class represents a mathematical entity (vector, matrix, imaginary number, mathematical set, et al) where less than might be a fundamentally reasonable operation, especially in some specific context.<p>His example is using it as an angle, where comparing two of them is conceptually pretty sensible.<p>If you pretend it&#x27;s a structure, sure, you&#x27;ll need to extract primitive data types out of it before doing anything with it. But if you want it to behave as a higher-level abstraction, reimplementing less-than (say, for comparing the vector magnitude) at every call site isn&#x27;t great.