In my experience, I've found that if you are a small company or don't have 8-10 seniors, hiring juniors is extremely risky, specially if you are not in the U.S. (or anywhere you can't fire them instantly when you realize your mistake).
One junior per 10 mid level to senior devs, and they can add value (given they are good) without taking anyone's time significantly.
One junior for 5 seniors can still work (specially if you arw a much bigger company and can move the juniors to different teams), but be prepared to have times where one of the seniors is spending way too much time with the junior... but hopefully, in a year or two, the junior will be mostly independent or at least will learn how to make best use of their time they spend bothering the seniors... if they don't leave the company in that time, that is, which they most likely will do because someone with a +1 year experience becomes much more valuable, specially as a junior.
This advice is too generic of course. I have also encountered juniors who have been a pleasure to work with, who will make sure to listen, understand and incorporate your ideas in a fast-paced way (juniors have the advantage of not knowing or caring about ALL the different things) and come back to you prepared with the right questions to make the best use of your time. But then these are not very common.
One junior per 10 mid level to senior devs, and they can add value (given they are good) without taking anyone's time significantly.
One junior for 5 seniors can still work (specially if you arw a much bigger company and can move the juniors to different teams), but be prepared to have times where one of the seniors is spending way too much time with the junior... but hopefully, in a year or two, the junior will be mostly independent or at least will learn how to make best use of their time they spend bothering the seniors... if they don't leave the company in that time, that is, which they most likely will do because someone with a +1 year experience becomes much more valuable, specially as a junior.
This advice is too generic of course. I have also encountered juniors who have been a pleasure to work with, who will make sure to listen, understand and incorporate your ideas in a fast-paced way (juniors have the advantage of not knowing or caring about ALL the different things) and come back to you prepared with the right questions to make the best use of your time. But then these are not very common.