Short answer: yes.
Long answer: in traditional publishing, money should flow toward the author. What does that mean? It means you shouldn’t have to write checks for reading fees. You shouldn’t have to write checks to cover postage, copying, and other office expenses. You shouldn’t have to pay a publisher to publish your book.
In traditional publishing, an agent will take a percentage of your profit. If you are offered an advance, an agent will take a percentage of that. If you earn royalties, an agent will take a percentage of those as well.
In traditional publishing, an agent only makes money if you make money. They offer representation because they like your work and they think they can sell it.
Is an agent worth the money?
You should never be in a worse position, financially, for having an agent. In many cases, you will be in a better position. An agent will earn back their percentage by getting you a better contract with better terms than you could have managed on your own. Your agent will place your manuscript in front of editors you wouldn’t have access to. Your agent will help you manage your writing career. Best of all, you will have a professional representing your interests, advocating on your behalf.
Why wouldn’t you want an agent?