There are many reasons for this inside the classroom. Some of the most important are eliminating downtime, showing that you are an eager student and feeding the energy in the classroom.
In life think about how the concept of quick take off may apply. It might be that you have a project that needs be done. The project may be for work, school or something around the house, even as mundane as daily or weekly chores. Quick take off could mean that you get to the task quickly without putting it off. It may mean that while doing the task you do it quickly and correctly without dawdling or daydreaming. It might mean moving from one task to another without the delay in between that can kill time and how efficient you are.
Many successful people are successful because they develop QT in all three of those areas. Which one of those areas could you benefit from moving a little quicker in. Be honest, and then make a decision to improve in that area. If it's starting, think about the gratification you're going to feel when the task is completed and as Nike says "just do it". If it's staying focused on the task at hand, get use to catching yourself and then say "Back to work" and get back to work (I've used this many times myself). If it's moving quicker in between tasks, then take an extra 5-15 minutes at the beginning of your day or the night before to plan out all the activities you must accomplish and then work from the list. Most successful people I know always work from a list. It's what allows them to be as productive as they are over the course of a day.