Agent As Patronus
I think a lot of writers have a clear understanding of what agents do on the front end of traditional publishing. Agents submit your manuscript to editors, secure an offer, and negotiate the contract. But I think a lot of writers are less clear on what an agent does after the deal is done.
Of course all agents work differently. Some may indeed retreat into the woodwork and not really be an active part of the process again until you're ready to go on sub with your next project. Some agents might be really hands on, and want to be involved in all the conversations you have with your publisher no matter how casual or inconsequential. Most agents, I think, land somewhere in between in a role I've come to think of as Agent as Patronus.
In Harry Potter a patronus is a magical shield of power and positivity that you can summon to protect yourself from dementors--the embodiment of negativity and despair. And I think writers should deploy their agents in a similar way during the publication process. An agent doesn't necessarily need to be CC'd on every single email. It's important that you develop a relationship with your editor, and sometimes that's easiest if the agent steps to the side until needed. And you will need your agent during the production process. As much as we'd like to think every publishing journey to be nothing but smooth sailing, the reality is that things go wrong. Maybe your publication date gets pushed back, maybe you aren't getting the updates or communication you expect from your publisher, maybe (and god forbid) you hate your cover. Sometimes things go wrong in a big, obvious way and sometimes an email just leaves you with a sick, hollow feeling in your gut and you don't know what to do. That's when you call in your agent. And do it first, before you do anything else.
For some things, even just talking to your agent will be enough to make you feel better. Agents are industry experts. They know when a hiccup or a road block is annoying but acceptable vs. when something really egregious is happening. Allow them to reassure you if they can, and trust them to guide you in the right direction (after all, you did your research before you accepted their representation. You've vetted them and know that they're experienced and capable).
But for other things, just talking to your agent isn't going to be enough. This is when your agent transforms into your patronus. Let your agent advocate for you. Let your agent be the one to broach difficult topics with your editor. This is what agents are for. They can be direct and tactful, and they can be objective. As the writer, you're probably deeply emotionally invested in your work and that can sometimes make it difficult to effectively advocate for yourself. Let your agent lobby for cover or title changes, let your agent chase advance payments or statements that are late, let your agent represent your rights and interests, and shield you. Part of your agent's job is to absorb all of the tricky bits so that you can maintain a working, positive relationship with your editor and publisher.
You get called out on social media for harmful representation? Don't go on a tweetstorm; talk to your agent.
You vehemently disagree with the notes your editor has for revision? Don't lash out at the editor over email; talk to your agent.
Think your book cover is the ugliest thing you've ever seen? Don't tell the art department so; talk to your agent.
Sensing a theme? When the dementors are coming for you, don't try to take them on yourself. Summon your patronus.