By enabling the FTE, you compare the performance of your agents on the same basis: for an equivalent presence time, you get the number of actions on messages that agents would theoretically perform.
Say, for example, Chris L is an agent. He logs in to the platform only occasionally to reply to messages that have been assigned to him. He does not categorize his own messages. He logs in only to reply, and then logs out. Suppose that given these facts, Chris L has no categorization or ignores, but has 9 replies over the selected period. Because of his short presence time, Chris L’s estimated number of replies/day is skewed data.