Also you can get metrics (key user action metrics) for this action, you can request by API these metrics or pin it to dashboard. All this functional comes if we have marked the action as key user action.
Also you will have key user action metrics for long time. (more info)
Also - there is an additional effect - for the Davis system - that we mark this action "important". You will have additional information if this action affected by problem\issue.
Sometimes Application have for example long searches-actions - and we marked such actions as key user actions to customize the Apdex thresholds - if for example - normal response time for "search" is 15 seconds.