After working with clients using LEM for almost 2 years now, I have heard the same concern over and again regarding the dreaded 'Activate Rules" button. (Primarily after a chasing-your-tail scenario where a client cannot figure out why their rule correlation isn't working when it works just fine in a filter)
From the LEM User Guide:
Whenever you create a new rule or change an existing rule, you are working on a “local copy” of the rule. The Manager has no way of using the rule change until you activate it. Activating a rule tells the Manager to reload the enabled rules it is working on, which allows it to upload up the changes you just made. You must activate rules whenever you create a new rule, edit an existing rule, or make changes to a rule’s Enabled/Disabled or Test On/Test Off status. Otherwise, the Manager will not recognize the change
While this is a great option to have if you have mutiple appliances and need to publish your changes, in a single-appliance architecture this button serves no purpose in practice. In all of the core Orion modules, creating/disabling/enabling alerts are now done with a single click through the new Alert Engine. This functionality should be uniform throughout all of the SolarWinds product suite. In LEM, when we save/enable/disable/test-mode a rule, that action should "publish" to the manager immediately and not require another submittal through the "Activate Rules" button.