I've been thinking about grammar recently, and its importance in the workplace. I do notice plenty of mistakes in other people's writing, and try to ensure my writing is correct. Some of my colleagues ask me to proof-read their emails and documents, and one or two others should ask, but don't.
When I receive an email or letter from someone new, I form an initial impression of the person from their style of writing, use of capital letters, spelling mistakes, apostrophes in the wrong place, and so on. This impression affects how I respond to the actual content I'm reading. Occasional mistakes don't have much effect, but several in a paragraph will make me believe that the sender is not very bright, where actually they may just be too lazy to check. As with most prejudices, this is unfair, and I should be more open-minded. My writing not perfect (and there's bound to be a mistake in this post), which makes it worse. Even so, if you are trying to sell me something, or persuade me to do something, bad writing will be an obstacle. You will create a better impression if your writing is good.
Many people don't care about grammar, and won't spot errors anyway. It takes time and practise to get better at writing. Is it worth spending much time on? It depends on who you talk to.