As a teacher, an editor, and a knitter, I see an awful lot of knitting patterns.
One of my most popular classes is the Project Class. It's a multi-week session that allows knitters to work on a project that is a personal challenge. I get all sorts of great projects in the class - new knitters who have knit a few scarves and are ready to progress to a hat; experienced knitters who want to learn a new skill like lace; and adventurous knitters who want to learn how to wrangle a pattern.
Knitters bring patterns from all sorts of sources - from published books and booklets, from magazines, and of course, all sorts of online patterns, freebie and otherwise. And I have to read through every one of them.
There are lots and lots of online sources for patterns - a thousand and one blogs, including mine, and all those self-published patterns in Ravelry and Etsy.
The problem is that many of them aren't good.
A student brought a hat pattern recently to one of my classes. She'd bought it on etsy, and I was shocked at the poor quality. Sure, the instructions were right, but it was missing key information: gauge and sizing. This disappoints me enormously. As designers, we're doing knitters a disservice if we're not providing patterns that are correct, complete and easy to follow.
Mistakes do happen, absolutely. Typos, incorrect numbers, editing slips. I've suffered from that myself more than once. (True confession: there was a minor mistake in the Vampire Sock pattern when it went live. We caught it pretty quickly, and fixed it, but it was there.)
But not providing sizing or gauge information is a major oversight. That would be bad in a free pattern, but it's absolutely unforgivable in a pattern that is sold.
I'm a little more forgiving of self-published freebie patterns - one of my students worked an absolutely stunning lace shrug from a pattern on a blog. It was a struggle - the pattern wasn't very well written, and there were a few pieces of information missing, but it was a freebie, and the author wasn't claiming that it was perfect, nor did she charge money for it.
In my opinion, any pattern - free or otherwise - needs to be complete and correct. Designers - please please please have someone proofread your pattern. And if there is a mistake, publish errata online. Please.
Incorrect patterns frustrate knitters. And frustrated knitters give up.
And if knitters give up, there are fewer of them out there knitting and buying patterns and yarn, and fewer designers can earn money, and fewer yarn companies can survive.
If people ask me about good sources for free patterns, I point them in the direction of Knitty (of course) and Berroco. I know that in both cases, the patterns go through technical editors - and therefore, they are going to be complete, accurate and well-written. It depresses me that I have to tell people to shy away from indie designers, but unless it's someone whose patterns I know and trust, I can't guarantee that the knitter is going to have a good time.
And after all, this is a hobby. It should be a good time.