How does Latin’s ‘sequence of tense’ rule work and why do I need to understand it?

In Latin, tenses are divided into two sets, or sequences: primary and historic. The main primary tenses are the future (I will verb), the present (I am verbing) and the continuous perfect (I have verbed). The main historic tenses are the imperfect (I was verbing), the pluperfect (I had verbed), and the simple perfect (I verbed). In Latin however we come across a slight difficulty as there is no distinction made between the simple and the continuous perfect as in English; therefore the single Latin perfect tense can fall into both primary and historic sequence depending on whether or not the verb’s action is completed yet.Why is this important?The sequence of tense rule is vital as it decides the tense of a subjunctive in Latin in a subordinate clause, for example, a result clause or a purpose clause. If the main verb governing one of these clauses is in the primary tense, then the subjunctive can go in either the present or the perfect tense, depending on whether the action of the subjunctive is happening at the same time as or after the action of the main verb (present subjunctive) or has already been completed (perfect subjunctive). If the main verb is in the historic tense, then the subjunctive can go in either the imperfect (if action is incomplete) or the pluperfect tense (if action is complete). So the rule is vital to reading and writing Latin.