There has been a lot of changes to the AX2012 system with the introduction of the retail module. However if you are not using retail should you disable the key to remove the functionality from your AX solution.
Recently I had a performance issue with posting a price journal. The journal was 200,000 records long, and the journal was taking hours to post. If you look at the code you would see the use of update_recordset and insert_recordset which are bulk insert command, but these only work if the insert and update methods have not been overridden. There was also some code in the posting routine to prevent the overridden insert and update methods being called, but only if NOT retail.
After switching off the license key (System Administration>Setup->Licensing->Licence information) for Retail Headquarter, the performance to post the journal was almost instantaneous.
There is however a side effect of switching of the retail headquarter licence key, when you synchronize the system you will get a number of warning messages related to retail tables. There is no way to remove them from the synchronization result list.
Ignoring the main side effect, if you are not using the retail module or any of the features, you should consider turning off the licence key to improve the performance of inventory transactions. As always you should test this in a non production environment to ensure it resolves the problem and works for your implementation,