The point is that if you give a number first, there is now an upper bound on your final salary but no established lower bound. If they give a number first, there is now a lower bound on your salary but no established upper bound. A situation where your compensation can only go up is seen as more advantageous than one where your compensation can only go down.
It's a trade off. If you anchor high you're saving yourself time from the majority of companies that try to underpay you. If you don't anchor, you risk getting your time wasted but eliminate the risk not knowing what you're worth.
If you are a highly in-demand, already highly-paid developer, it is likely in your best interest to anchor high. If you are a junior level and trying to get a middle-level role, it's probably better to not anchor.
i think the problem comes if they put out a lower bound that is way too low, then there is no way for them to accept a much higher salary without looking stupid, so they wont.
