Training drains the employee's power bar. There are many training methods that your employees can use, with more and more being unlocked as you progress through the game. As such, the stat increases from leveling up come at a high cost compared to training so, the main reason to level characters is to unlock genres and types or switch to a better career. Salaries grow at a compounding rate: each level up multiplies the salary by 1.2. Normally this means having level 5 in all jobs, but employees that start as Director or Producer can circumvent this. Once an employee is level 5 in both Director and Producer, the Hardware Engineer career becomes available to that employee, and you may begin working on Console development. Through the use of the Career Change Manual available from the traveling salesman, you may choose an employee to change careers, and begin leveling them up in each career.
Leveling your employees requires Research Data ( ) and raises both employee stats and salary. More information about careers can be found on the careers page, but a list of careers is: Some require specific unlock conditions, but all employees start off with some job. There are a total of 8 different careers, with different pros and cons.