It could make sense to use a cheap model to decide if you need to run a long, high effort or otherwise costly effort. Then you can take many decisions at low cost, but think hard when it’s time to make an important decision.

You wouldnt normally use a dumb model as a personal agent to get a smarter model to do work, but you may make use of that mechanism in some kind of automation process.

But there are definitely cases.

GPT Pro is an absolutely spectacular model, that almost cannot be used without 'prompt help'. Or rather, it can only be effectively leveraged by very intricate prompting, which requires the help of another agent.

I typically use Claude Code to write prompts for GPT Pro , and cut and paste the prompt in, and let GPT Pro work for 20 minutes, then take the response back to Claude Code and work with Opus to consider the results.

Opus is 'dumber' (nominally) then GPT Pro.