If you have a parameter assigned to a group or environment, and you've only included a single value, you can hide this parameter and use the single value as the default for all VMs created in the given group/env. This is a powerful feature that can be used to accomplish such tasks as routing VMs to certain networks, datastores, etc. It can also be used to bind specific policy decisions to environments. For instance, you might bind a "3-day backup" policy to a dev environment and a "1-month backup" policy to a production environment using a parameter that contains a list of backup policies. By binding this parameter to an environment and removing all but the policy you want to use in the environment, you're effectively saying: All VMs in this environment should use THIS policy. Following with the KISS rule of server provisioning -- the less options on the form, the better, so because there's only one option bound to the environment, the user isn't prompted for the backup policy.
When the parameter is user-defined, go to Admin/Parameters, find the parameter and check "Hide single value", and SAVE. Note: This label is subject to change in the future. Now if only one option is presented in this parameter, it will not be displayed to the user, but will be chosen by default.
The "Hide single value" property is also available to system parameters, but it isn't presented via the CB UI. To set this property to TRUE, go to Admin/Database Browser. Find the link to "Custom fields" under the "Infrastructure" heading. In the list presented, find the parameter you want to edit, and click it. In the resulting form, you'll see a checkbox for this option. Check it, and click SAVE.
Let's say we want to hide the network if there's only one network available and the IP for that network is assigned via DHCP or a Pool of IPs. Following the "System-defined Parameter" instructions above on the NIC1 customer and setting the "Hide single value" property to TRUE will accomplish the goal.