A Manual Computer Group is a group that is defined by manually selecting the computers from the Computers List Panel1. A Manual Group can only be shared between Master Operators2.
An Automatic Computer Group is a group that is defined by using Relevance expressions or properties to indicate the group membership3. An Automatic Group can change its population dynamically depending on the evaluation of the group properties3.
An operator might create a Manual Computer Group instead of an Automatic Computer Group if they need to base the group membership on information that is not available using Relevance expressions or properties. For example, if the operator wants to group computers based on their physical location, owner, or usage, they might not be able to use Relevance expressions or properties to determine that information. In that case, they can manually select the computers that belong to the group4.
However, Manual Groups have some drawbacks, such as being static, not scalable, and not extensible5. Therefore, it is recommended to use Automatic Groups whenever possible and use Manual Groups sparingly25. References:
Manual Computer Groups - HCL Product Documentation
Manual Groups vs Automatic - Platform - BigFix Forum
Creating Automatic Computer Groups - HCL Product Documentation
Task or Fixlet to move computers into manual group - BigFix Forum
Regarding Manual Computer Groups - BigFix Forum