Developers are smart, but they're not mind readers. If you hire a developer to help build your site, you'll need to articulate your vision as clearly as possible. If a developer doesn't understand what you want, he or she can't build it.
At the same time, this doesn't mean you need to make every possible decision about your website. Many technical decisions are best left to your developer. You don't micromanage your plumber, right? Unless you're ready to delve into the world of PHP, CSS, SQL, and all those other delightful acronyms, know when to delegate technical decisions.
By some perverse psychological law, these technical decisions can sometimes slurp up a huge amount of (billable) conversation time, while the details of what the site will actually do remain hazy.
Developers can be great conversationalists, but if you're going to procrastinate, spend the money on a movie. Or putt putt. Whatever. When you're working on your website, focus on the decisions that only you can make, that your developer needs you to make. Delegate the rest.