Why is there two different settings for PCoIP Session Variables and which should I use?

Overridable Administrator Defaults contains settings that specify PCoIP session variable default values, which can be overridden by an administrator. These settings write registry key values to HKLM\Software\Policies\Teradici\PCoIP\pcoip_admin_defaults.

Not Overridable Administrator Settings contains the same settings as the Overridable Administrator Defaults folder, but these settings cannot be overridden by an administrator. These settings write registry key values to HKLM\Software\Policies\Teradici\PCoIP\pcoip_admin.

Local machine settings are held in the registry keys in HKLM\Software\Teradici. If the same registry key is present under both HKLM\Software\Teradici and HKLM\Software\Policies\Teradici, the group policy setting in HKLM\Software\Policies\Teradici overrides the local machine value.

I prefer setting the PCoIP Session variables as “Overridable”. You are using these settings per pool basis via GPO to give the best overall experience for your users. This will allow you to cater to most of your users but allow for some flexibility for the odd use case that tend to crop up. If you start implementing a hundred and one PCoIP GPO’s you will have more to maintain during upgrades and more to troubleshoot.
The flexibility comes in the form of using different settings on your zero client and soft clients. Zero clients are easy to make different settings but the software client can be changed with a text file. VMware KB -> http://kb.vmware.com/kb/2015292 has the full steps to create the text file. The below steps are from the KB article.

1. Create a file called pcoip_client_settings.txt using a text editor such as notepad.exe.
Settings in this file only take effect on the client.
2. Save the file to C:\Documents and Settings\\Local Settings\Application Data\Teradici
where is the login user ID.
3. Enter they key/value pair for the session variable that you want to override.
Enter one key/value pair per line, seperating the key, ‘=’ character, and value with spaces.
For example: pcoip.device_bandwidth_floor = 1000