You can use customization specifications to define the configuration settings and parameters for customizing virtual machines during the deployment or cloning process. PowerCLI provides two types of objects for customization specification: persistent and nonpersistent.
Persistent Customization
Persistent customization specification objects are stored on the vSphere server. All persistent customization specifications created by using vSphere Client or VMware PowerCLI 4.1 or later are encrypted. Encrypted customization specifications can be applied only by the server that has encrypted them.
Nonpersistent Customization
Nonpersistent customization specification objects exist only inside the current PowerShell process. Nonpersistent customization specification objects are not encrypted, but cloning them to a vSphere server encrypts them.