I have played about 15 hours of Game Dev Tycoon and haven't really paid attention to training my staff. What I'm curious about is how much exactly does 1+ speed or 1+ research actually do, and is it worth training staff when I can just keep hiring new staff?
The higher the number in research, the higher the amount of research bubbles (i.e. helps you to have more research points, which helps you to research/train more).
The higher the speed of a developer, the Speed increases ratio of bubbles that are produced.
It depends. In the beginning hiring new staff is more efficient, as you will get better results and don't have to invest a lot of research points for training. But at some point you have to start your own training to specialize your staff. Starting there, you have to continue training on your own to achieve better results.
I started training my staff once I had 2 new employee's. It doesn't take an age to increase their focus to 300. maybe 3-4 training sessions. Its worth it.