Process batches are useful for keeping the history of bulk changes made to a specific group of inventory. If you're a single person operation, you may be fine with bulk editing straight from the Inventory Page. As your team grows, it can save time to have a recorded history of who made which bulk changes.
Some examples for why you'd use a process batch:
Unlocking
Changing the grade or damage conditions after physical repairs
Updating the status of a group of devices that have physically moved
First off, create a new Process Batch from the Process Batches page:

You can set a Description and a Status for a new Process Batch.
In this example, we'll be unlocking a group of AT&T iPhones.

Once saved, you can add inventory to the Process Batch by clicking on the blue + button:

Paste a list of ESNs or IDs of the group of devices you want to add into the pop-up window:

Once you've added devices, you can make bulk changes from the action menu:

Any changes you make will be recorded on the process batch itself:

And on the individual devices themselves:

That's it! You just made a Process Batch and edited a group of devices.