I mean, our juniors were useful. Sometimes they got easier tasks, sometimes they got tasks on non-core parts of the project where the stakes were lower. I think that when they are truly just useless, they are either on the wrong project or company do something wrong.
I did things, some of which were pretty useful or clever, but between telling me what to do, coaching me how to do it, reviewing what I did, and telling me what to change, I probably cost more time than I saved the first few years of my career.
I almost certainly took more time from my seniors than I saved them, and the juniors I've mentored have mostly done the same for me.
