Verb tense conveys an action’s time zone: past, present, future, and so on. Rules that govern tense help ensure that whenever someone relates a series of events, they do so in a way that’s consistent with the actual chronology of the events. Just imagine how confusing a passage would be if verb tenses were used willy-nilly:
All employees will review the safety policies and procedures before the accident occurred, but no one at the scene of the accident were following procedures.
Consistent use of tense clarifies the timeline, indicating when each action occurred in relation to the other actions:
All employees had reviewed the safety policies and procedures before the accident occurred, but no one at the scene of the accident followed the procedures.