Verb tenses establish TIME. There are documented cases of people who misused verbs and put themselves in places at the wrong time and have spent some time in jail as a result.
In a nearby federal prison, there once was a corrections officer who did not have a good command of English grammar and verb usage. When he had to document an incident involving the misconduct of an inmate, he used inaccurate verb forms and tenses. So, when the inmate went to court regarding an extension of his sentence because of his behavior in this incident, his clever lawyer was able to get the case dismissed because of the officer's incorrect verb usage. For, the inmate was elsewhere at the time the tense the officer had used. indicated.
Also, in the medical field, exact documentation--this includes tense uage--is paramount since medical documents can easily end up in court in malpractice suits, etc.
I agree. It really is a sign, to me, anyway, of appreciation and respect for language. A whole lot of people speak as you've all described, and it's annoying but not worth noting, really, because it's just who they are. I'm always stunned, though, by otherwise articulate and savvy people who say things like "should have went." What a note of discord that strikes in me, even though it's the most common verb tense error from my perspective. And it's a tough habit to break, it seems. Proper grammar and effective vocabulary, I believe, are the hallmarks of people who read and/or write.
Verb tense is important because it signals time. By using the incorrect verb tense or by switching verb tenses, it can be confusing to the reader. Obviously, it would be important in business communication because of the time-sensitive nature of many documents that are composed in the business world.