This is something that will vary so much by circumstance and individual situation that I'm not sure rules of thumb, or what other people do, will help much.
I will say that when my department had significantly less junior staff than senior staff, things seemed to run more smoothly. However, we were spread across multiple projects, sometimes part time on several, so it's not quite the same situation.
We recently had a project where much/most of the detail design & documentation was done by (a series of) interns. They had one experienced designer working with them. They then had the project manager, project systems engineer, and line manager guiding them on what they should be working on & how. Then just to confuse things more they also got some 'supervision' from and optical/mechanical engineer, a lead development engineer (or whatever his title is - think big brain socially awkward). Then they also had a related but for some reason mostly separate team working on another aspect of the project, which consisted of another series of interns and another manager, who'se electrical by background but loves to dabble in industrial design and the like.
Then, on occasion, when someone really had to get their poop in a group to actually get something released so we could start manufacturing, I'd chip in and crack the whip/take on some complex tasks.
With all the managers & senior staff coming from different view points etc, the people actually doing the work sometimes got conflicting direction.
This was night marishly inefficient.
KENAT,
Have you reminded yourself of faq731-376 recently, or taken a look at posting policies: