The word on the web is that due to the way APFS handles file extents, a VM can create tens of thousands of extent entries in the file representing the VM as time goes on. For example see the OWC presentation at last year's user conference. The issue can cause a ballooning of access time since APFS is a tree structure that needs to be traversed. The issue also causes massive fragmentation - not an issue on SSD drives but death on HDDs. In fact the recommendation there is don't use APFS on rotating media. Parallels - any comment? Any help on alleviating this issue?