As I've mentioned, I don't have an agent. Many of the folks here at YA Stands do, however, and I hope they'll chime in to correct or add to what I'm saying. I'll probably be following this up in a couple of weeks with more information.
I haven't called this a pros and cons because I was having trouble thinking of any cons to having an agent. I guess wait times could be longer, because you have to wait for the agent to respond to you and then wait for them to submit your manuscript to publishers and for the publishers to get back to the agent, who then has to get back to you. On the other hand, agents sometimes have connections at publishing houses, which means they might hear back sooner than an author who's submitting cold.
Those connections are one of the pros of having an agent. Agents also can submit to publishers who don't allow submissions directly from authors, which includes many of the largest houses. If you have your eyes set on the big names, you'll need an agent. And because of the connections they have, agents may have more up-to-date information on which editors and companies are looking for your type of story, while the writers guides may be outdated.
Agents know how to negotiate. As an author, you might be able to get a small advance, and you might be able to negotiate it higher. But an agent can potentially net you a much better deal than you could get on your own.
Agents add another level of quality control. You've written and revised your manuscript. Your critique group and/or beta readers, if you have them, have gone over it with a fine-toothed comb and you've revised more based on their suggestions. And now you're ready to submit. An agent adds another set of eyes, one with experience in the publishing industry (something your crit group and beta readers may or may not have), and can help you really drum that manuscript into shape.
There are a lot of benefits to having an agent, and I've only mentioned the most obvious (to me) ones here. Those of you who have agents, please feel free to chime in with benefits you've found.
There are also things to be wary of when it comes to finding an agent, and I'll discuss those in my next post on February 13.