Matt Pocock tweeted a good frame for why subagents matter:
The dream for any coding agent is to do the same amount of work for fewer tokens. That means more time in the smart zone (first 40-50% of context). Subagents are so elegant a solution that you'll see them everywhere, forever.
The "smart zone" is that first 40-50% of the context window where the model is sharp. Past that, things degrade. The model loses the thread. Context rot. It happens gradually.
Using subagents can prevent a lot of needless context from entering the main thread. By delegating tasks to other agents, the context stays cleaner and stays in the "smart zone" for longer.
A similar idea is behind Ralph loops where each task gets a fresh agent, avoiding accumulated baggage from previous work.
I think about this a lot when using Claude Code. I delegate to subagents regularly now because it keeps each context focused.
If you're interested in AI agent feedback loops, you might be interested in my post on evaluating our test pyramid.