Knowing that it was half a century after the reformation but before the English civil war, yet after the establishment of other colonies is important.
Knowing that it was 1620 rather than 1619/1621 isn't important - but that's all you are tested on. Treating it as maths where being 1year out is completely wrong is stupid.
1) A practical one: suppose you would be lenient on a test and allowed the students to be 5 years off. How much would that change? How many students are actually only a few years off? Is 5 years reasonable or should they be allowed to be 7 years off? What about the situation where a set of events are closer in time than your deviation?
2) One from generalization: if you have to know it was half a century after the reformation, you still know nothing if you don't know the reformation started in 1540 (I'm making this year up; it depends much on the country). Which still doesn't mean a thing if you don't know Michaelangelo died in 1480 (still making stuff up), which is 400 years after the Dark Ages started (...). Do you think they should know whether Raphael and Thomas of Aquinas lived in the same times? Should they know whether the Austrian-Hungarian empire existed already when Newton invented gravitation? The more facts you start relating, the more important precision becomes. The more you want to describe detailed chains of events, in which the details matter, the more facts you need to relate.
That's what happens if you teach the facts devoid of the relations. The history classes where they taught relations I got something out of. The others are just useless footnotes in my education.
