Normally if you don't file I-539 to extend your B-2 status, it will not affect you to apply for the new visa to come to US again, but the current B-2 visa stamp on the passport will be void even if it does not expire if you leave US after the I-94 expires. Thus you need to apply for a new visa to reenter US in the future.
If you file I-539 to extend your B-2 status and leave before the extension is approved, then the current B-2 visa will be still valid even if you leave US after the current B-2 I-94 expires. Thus, you can use this visa stamp to come back to US in the future, not need to apply for a new visa.
