You may have developed some Actions which are primarily for the utilization within other Actions. These are normally developed for modularity purposes and may not have any significance from business point of view. Such actions, if presented while creating the scenario, may confuse a business user and could create unnecessary clutter.
You can turn-off the visibility of such Actions for a Scenario. By default, every action is visible from Scenario. You can turn this off from the Action sidebar as shown below.
Note: This is an advisory flag. Turning the visibility to "off" does not affect existing scenarios in any way. If this action was already used in some of the scenarios, they will continue to function. When building a new scenario, this action will not appear in the step selector list.