Agents I respect do this.
Here's a recent post by Jill Corcoran that I found via the nicest, most courteous agent in the biz Rachelle Gardner, and she too has this policy.
I profoundly disagree with the premise they use to justify its use:
1. It takes too much time to reply.
That means you haven't figured out yet how to simply your process. I reply to every query. It doesn't take me hours. I have an auto-signature that is the text of the reply. I click reply, I click "sig-query no" from my five options, and click send. Total time: 3 seconds. If you get 100 queries a day, that's 300 seconds to reply. Do the math: 5 minutes.
Don't personalize it with their name. Don't type in anything extra. Just click the auto-sig line and you're done.
What, you can't do this? Your mail management program doesn't allow it?
Get a new mail management program.
Now, it takes longer to READ the queries than it does to respond, but I'm assuming we're both reading the queries. It's only the response time that's at issue.
2. Authors write back with questions/complaints/tirades.
So what? Ignore them. Delete them unread. You don't owe anyone more than that. I've had my share of those too, and these people don't deserve one second more of your time than it takes to delete them.
Further, "no response means no" is a BAD BUSINESS PRACTICE. Who do you think writers are? They're READERS.
If I invest five minutes a day in not making writers feel like they don't matter, I'll have done a good thing.
If I invest five minutes a day in not alienating potential readers for my client's projects, I'll have done a better thing.
If I invest five minutes a day in writers who may query me again with projects I do want, well, that's good for me too.
And you know what? Some writers actually prioritize their queries by who replies to everything. That means *I* get first shot. Come to think of it, why am I telling you this? If I work this right, I'll get all the good stuff first!