But with Phil Steele it's more than that. It's can you let me read it without looking at a list of your made-up acronyms.
After several years of keeping Steele's preview next to the shitter, I can read Phillese with no issues.
If you think about it, it is incredibly important though. Especially if your job is all about the communication of ideas and information. Which is most jobs.
When I was younger, I would bring a red pen to interviews and start marking grammar and spelling on resumes while the candidate talked about his or herself.
I hated comp professors that left papers looking like they were graded at a ritualistic hog slaughter.
I actually think proper grammar is a bit overrated. I might judge people on some things, but I myself put the sentence-enderer outside the quotation marks on purpose, because the actual rule is stupid.
I like proper grammar in a lot of contexts. I have strong opinions on some grammatical rules (Oxford comma!). But there are some rules that aren't worth it. Like the rule that prepositions are inappropriate to end sentences with. There's no ambiguity or difficulty in understanding introduced when you stick a preposition on at the end. Somebody just wanted English to imitate Latin, where the preposition always has to precede its object. Which is dumb. English ain't Latin.
Depends on what we are talking about. A message board? Doesn't mean anything. My spelling and punctuation sucks here. But if your resume, something you should have spent hours on, has basic grammar errors that tells me you aren't one who shows attention to detail.