According to Microsoft Docs, when you
Mount-WindowsImage, you can add the
The Optimize parameter reduces the amount of time it takes to initially mount the image. However, processes that are ordinarily performed during a mount will instead be completed the first time that you access a directory. As a result, there may be an increase in the time that is required to access a directory for the first time after mounting an image using the Optimize parameter.
I can test this in PowerShell using the following script to see how much longer it takes to Mount a Windows Image without using the Optimize parameter
I initially ran the script after a clean boot. After the first test, I swapped the processing order and rebooted to run the script a second time.
Win10 1809 x64
Win10 1809 x64 Optimize
As you can see the results were quite the opposite of what I expected according to the Microsoft Docs.
I cannot recommend using the Optimize parameter when mounting a Windows Image, add this to the fact that in Windows 10 1809 you cannot remove Appx Provisioned Packages offline when using Optimize