When writing isn’t clear, it becomes a double waste of time.
It wastes the time of your reader, who has to puzzle out what you mean.
And it wastes the time of the writer, who will either not be read (so what was the point); or he will have to write it again, to explain what he means.
Writing properly means communicating clearly. It doesn’t necessarily mean obeying the rules correctly. It means getting your point across so the reader clearly understands you.
To get your meaning across clearly, you need to choose the right words and set them in the right order. After that, style will take care of itself. As Matthew Arnold (An English Victorian poet) said:
Have something to say and say it as clearly as you can. That is the only secret of style.
Choosing the right words to use is not always easy, however. Often it requires a little work and a fair bit of thought.
Clear writing, like clear thinking, is hard work. But it is work that is worth doing, because without it, you waste not only your own time but also that of your reader. And that is a rudeness which is inexcusable.