This is a thing that I’m sometimes so obsessed with and never-the-less sometimes I manage to neglect. Grammar and spelling is indeed very important, it reflects on one side your capability to focus and your attention to details, but on another side, because of the effort that you made or did not make it also reflects your attitude – responsibility and care about what-ever you are doing – writing about.
Never-the-less, I have always thought that the content is way more important, and is more ignorant to ignore a good content or have a lower attitude towards it because of such mistakes. These days our focus is spread in multitasking like never before, there are tons of visual, audible or plain psychological distractions. These do not affect us just  directly whenever we might find ourselves typing, but can easily contribute to tiredness which again isn’t so productive for our focusing capabilities.
I suppose we are adapting creatures, and it is a sort of survival of the fittest one way or another. Technology is helping us with auto-correction but it can fail, I don’t always want to write “i donut kink munch about it” (that phrase did not get corrected – wasn’t underlined). But specially if it’s something that will be public, do take the time and do it right.
Do realize that there are two extremes in this: on one side you can miss important moments or opportunities by not expressing yourself as directly and fast as possible or at all – I’m saying this because in many things it’s a competition out there and the one that’s first is favored; but also the one that is best is favored and so on the other side – not realizing what you actually express and how you express it can have an unfavorable outcome.
This perspective and these extremes are important not only for the stuff we write, but also for things we say or for behaviour we have, choices we make; it comes as an incentive to think before we talk or act – exchanging perspectives (hats or shoes or roles with the others involved, or with the world like Kant would suggest – how ever helps), using critical thinking / skepticism too / questioning everything – including our own premises / conclusions.
Of-course, there’s more.