I didn't notice any significant change in context usage, and tasks were completed faster. That surprised me, I'm still not sure (not an expert on this), but maybe the handoff boundary was the problem. When the main model gives an isolated task to the subagent, the latter goes wild producing a comprehensive report, trying to satisfy every possibility. Without the handoff, the main model does the job much more precisely and conservatively, checks only specific/narrow things, and stops sooner.
Recently I decided to reintroduce 2 subagents to see how it goes. First was to have a cheaper model drive my real Safari browser instead of using agent-browser and the like. Second, to see if having a cheaper model navigate/search my file system helps in any way.
I think there's some benefit to having a cheap model drive Safari, because there's so much unavoidable garbage produced in that interaction. The filesystem one I don't think I see any benefit, just a lot of unnecessary work that (albeit cheap) wastes more time.
Of course I'm eyeballing this, not benchmarking formally, but I see so many people just onboard these mindlessly. Are you sure that you saw a real improvement in the produced outcomes/timing, or was it based on seeing subagents do a lot of stuff and assuming that the main model would've been doing the same at higher cost?
I admit that subagents may have great benefits, but I wouldn't treat it as just out-of-the-box basic feature that always improves your outcomes.