The prime function of language is to enable information to be communicated from one person to another. If the form of that communication is the written word then spelling and grammar play an important part in ensuring that the reader of the communication understands the message the author of the communication intended to convey.
That said, however, the human brain – even when registering that a word has been spelt incorrectly or that the grammatical structure of the sentence is wrong – will nevertheless ignore these errors and seamlessly interpret the communication exactly as the author intended.
To one – [no need to mention names] – who cares deeply about language, though, being confronted on a daily basis by mis-spelt words and ungrammatical sentences is a sore trial . . .