Position Management enables structural stability, budgeting, and headcount control. The position structure is independent of employees - it represents the budgeted positions in the company. So essentially, when you hire a person you need to have the budget to pay for that person as well as defined job description/roles and responsibilities. Position management enables all of this to be managed in a structured way. For larger enterprises, this is critical for fiscal management, budgeting, and operation.
You then of course have succession planning and recruiting, which rely on positions. You can recruit for a job, but it is much more generic.