Misspellings can distract, annoy or confuse the reader, drawing attention away from the real message. But some typos matter more than others, depending on the context of where the typo occurred.
Business Websites
Spelling mistakes on a personal blog don't have the same impact as the mistakes that appear on a professional site. Typos on a business website offering services or products can give the reader a number of negative impressions, including the company doesn't care about its customers, isn't competent, and doesn't pay attention to details. A whale watching tour company would probably do more business if their tagline didn't read, "Come see a wail today!"
On Merchandise
I worked for a printing company specializing in promotional merchandise as a checker, which was essentially proofreading the customer's order. It sounds pretty boring right until you realize that if the business phone number has been printed incorrectly, the 1,000 calendars intended to promote the person's appliance store will be useless. Justin Bieber experienced something similar when the word "purpose" on official Purpose World Tour merchandise was spelled "purose."
Password Instructions
I monitor social media sites for several of my freelance clients. This involves passwords. Being paid through e-transfers is also password protected. When a password appears in email instructions all lower case, but the website or transaction password has been entered differently into the system, I am denied access.
Crawlers
Search engine crawlers search websites for up-to-date data and working (not broken) hyperlinks. While each search engine has its own set of criteria, all of them, particularly Google, seem to value quality content - poorly constructed sentences, misspelled words, and mediocre presentation can hurt your page ranking.
Headlines and Titles
The whole purpose of a news headline or article title is to grab the reader's attention by revealing what the story is about and to keep the reader reading. Typos can make a headline unintentionally funny or just plain confusing, grabbing attention for the wrong reasons.