There is only one enhancement in Projects Billing. This enhancement is to address grouping of the adjustment item. In prior releases, the adjustment item is billed in a separate credit memo. But now you can control how you want to bill this adjustment.
Here is an example:
Customer was billed for Task T1 : $100
Then the item for that task was adjusted and moved to Task T2.
Now a reversal for Task T1 is created under a new credit memo for <$100>
A new standard invoice for Task T2 for $150 (for new rate) is also created.
In 12.2, you can group the adjustment (-$100) and also the new item ($150) together in one invoice.
There is an option in billing setup form for this and it has to be set.