What happens if you watch TV and do not do your homework?

One time: nothing really.

Five times: you'll have to make it up.

All the time: you might have to redo the grade.

It will lower your overall GPA about 20% in most schools.

The benefits of doing homework mainly center upon the linking of the activity in question to the storage media (brain). This then allows the brain to remember the activity and therefore increase the efficiency of the activity. For example maths homework for school age, is quite repetitive, by doing these repetitive exercises the brains ability to recognise the structure of the question and answer the question quickly is enhanced.

So by not doing your homework you increase your chances of not being able to achive your best in exam or time constrained situations.