Selling is another matter entirely. If you would like the peace of mind to know that your home is actually in your past once the money is in your bank account, use a broker. Having your past home haunt your future can be a miserable prospect.
The broker is causing the closing to happen by finding and satisfying the buyer along with the buyer's many, many issues with most properties.
They actually only charge 1% commission as the selling agent now, too, so vs a typical 6% combined commission, they save 33% for the seller. (Assuming just a sale)
Redfin doesn't seem to disclose how they calculate the refund anymore, though, so I'm not sure how much that works out to be. Seems to be around half a percent, so lower than it used to be.
All combined, it's close to half of the traditional fees that they either refund or don't collect.