"Germans are always punctual – only the Swiss are more punctual!"
You may have heard this stereotype before. Often, people who don't have contact with Germans or Swiss make generalizations like this.
There is no question that punctuality is taken more seriously in Germany than in many other parts of the world. Appointments are commitments, especially in a professional context.
When you are doing your training, going to the doctor or at work, you should be punctual. You could run into problems if you make your boss, your colleagues, or customers wait. It is also impolite to arrive late when meeting friends. You should at least call if you know you're going to be late.