At my company, we use Alfresco to store the documents of a large system. In our solution, the users never access the Alfresco UI (share) directly. They only interact with our system and the backend of the system calls Alfresco API using the CMIS standard. Because of this, we have only a single user in Alfresco, which represents our system.
We have too many documents stored (3 millions of "active" documents, 5 millions if we count old revisions and deleted content), but we're running low on hardware and suffering from poor performance. During our investigation to see what can be done to increase system performance (while waiting new hardware acquisition), we saw that Alfresco is spending a good amount of time checking ACL permissions. The prints below shows the impact of an HTTP request and a database query regarding overall system performance.
Since we have only a single user (from Alfresco's perspective), we though about disabling this checks.