I had an agent once. Then I had another agent. Then I had the first agent again. Then I had no agent.
Recently I was offered the chance for a new agent. I'm sitting on the fence, trying to decide which way to jump.
On the one side are people who say that the old system is breaking down, and authors don't need to become cogs in the machine. They argue that you have more freedom as an author if you go it alone: you write what you want to write and let the people who publish that type of thing work with you instead of writing what some Bighouse Publisher thinks the world wants to read.
On the other side are the people who are actually making money, because those Bighouse Publishers print in tens of thousands rather than hundreds of books. Those people generally have an agent. (Before you start writing that comment, I know there are exceptions, people who make a ton with an indie book. They're widely discussed and seldom imitated.)
So the arguments go back and forth. Agents take a percentage, and at least in one of my past experiences, do nothing to earn it that I couldn't have done for myself. But there's always the hope that an agent will know the editor who is looking right this minute for exactly what I just wrote. That's why they're worth that percentage-- when the system works.
What I have decided is that I'm operating from a much better position now than I was when I dealt with the first two agents (one of whom dropped me. The other I fired, but in the nicest possible way.) I know the business better now. I have some successes under my belt that make me a desirable client rather than a "Please Sir or Madam, will you read my book" type. I know that an agent is supposed to work for me, not act as if she's doing me a big favor by reading an occasional email. And I know what a good one can do for my career if I decide I really want to enter the larger stage and take on the pressures of Advanced Writing and Publishing. With this knowledge, I plan to meet with my prospective agent soon. When that happens, we will meet as members of a potentially productive team, and I will be every bit as ready to say, "Not for me" as she is.