Every SalesForce instance can sustain a maximum of 5 Apex jobs simultaneously. When a Batch is committed, an Apex job is generated to process the Batch. A Scheduled Apex job is also generated to check how many processing slots are available. If there are no slots available, then another Scheduled Apex job will be generated 30 seconds later until it finds an open processing slot. This is why you might see multiple Scheduled Apex jobs for a single task, such as a Batch commit.