Do they really matter.
Not a great deal. However, there are times when a typo or spelling error can change the entire sense of a message. In this case, it really does matter.
I've pretty much given up on people whose first language is not English who get confused between the preposition 'to' and the adverb 'too'. I've done it myself, and not always caught it. One of my most common typos is 'and' for 'an'. This is probably because of my silly fingers and their learned behaviour. I've been a touch typist for about 60 years now, and the hands get into bad habits.
Then, of course, English is full of homonyms. Words that sound the same but have different meanings. My favourite example: "The peer peered down the pier to see if there was a boat in the dock". This very loaded example has three words that have different meanings, two with the same spelling. English can be such fun for people with it as a second language, eh?
However, when you put something in writing, it represents you. Under such circumstances you should always try to put your best words forward, would you not say?
People who try to make English spelling work by the look-and-say method are in a very leaky boat indeed. English is anything but phonetic. Consider the word 'ghoti' which is an alternate spelling for 'fish'. 'gh' as in cough, 'o' as in women, 'ti' as in attention. This was pointed out by George Bernard Shaw. And I am sure we've all seen 'My Fair Lady' which is a version of Shaw's 'Pygmalion'.
The main problem with English is that it is full of portmanteau words as pointed out by Charles L. Dodgson (Lewis Carroll). Usually such words are not only two or more other words jammed together, but often they are imported from some other language. You see, English is a living, modern language and as such it tends to be a polyglot. The only language I am familiar with that doesn't steal from others is Latin, and that is because Latin is completely out of use.
"Latin is a language as dead as it can be.
"First it killed the Romans, and now it's killing me."
Schoolboy chant.
Well, folks, the nice thing about Latin is that there are things you can't say in it because it went out of use as a vernacular tongue sometime in the late middle ages, so all our nice technical progress is missing. I do assure you however, that the language has as many or more 'dirty' terms and phrases as any modern language and some that simply don't bear repeating even in impolite company.