Scorekeeper strategy will keep a score for the node, that is always larger that 0 and is in-/decreased by the state of the monitored checks/node. Only if the score reaches some configurable threshold an alert will be sent. Immediate strategy will send a alert immediately when a monitored check/node is in a bad state. ScoreKeeper is best used for checks that should have some kind of fuzzy thresholds, like ping check where a couple of failed pings is usually not of any concern. Immediate is used for something like LogChecks where a log file in a bad state should be alerted immediately.