Posting 10 pages in SYW won't hurt your chance of getting published. It is recognized as a place to get feedback, not necessarily an ego-feeding.
Posting large excerpts on one's website or blog: you can get away with more pages, but you're in a gray area there. If access to the book is limited to specific friends with a password to get in, you're okay. It is better to not make it available to just anyone who surfs by. That can include trolls and scam artists looking for a victim with a wallet they can empty.
Quoting a few hundred words on a blog won't hurt, but I'm not sure why one would bother unless it's the opening page of the book and you're asking "Is this a good hook?"
In writing terms that can be the dangerously loaded "Do these pants make me look fat?" question. It takes a brave person to provide a truthful reply!
Once a book is published, you can advertise with lengthy excerpts on a website. I've got three of my novels up, with about one-half of each posted. The idea is if the reader wants to finish 'em he can click on the link to an online book store or the publisher and buy!
Most writers usually post only a couple chapters of their published works. I'm into overkill!
One of my friends has a successful series and wrote some short stories for it specifically to post on her website. They not only give a complete sample to new readers, but tickle the heck out of long-time fans. She never intended to sell them anywhere, but they've earned out in getting more people to buy her stuff.
But do that kind of thing AFTER you're established!