It matters because it is what makes service repeatable when the person who knows how everything works is on holiday. An MSP that grows past a handful of technicians without it discovers that quality varies by who answered.
The common misunderstanding is equating it with the software. Buying a service desk tool gives you a place to record work; it does not tell you who owns a service, what it promises, or what happens when it degrades. The tool is where the practice is recorded, not where it comes from.