They are a convenient way of dividing the period from when the aircraft starts it's takeoff roll to levelling in the cruise. They will include getting airborne to a height to clear a mythical non existent obstacle (screen), inial climb to get clear of the ground, reducing from take off thrust (either full thrust/power or reduced), reconfiguring from take off flap setting to clean, climb at atc constraine speeds, free climb at econical speeds.
Yes, the go around will have similar divisions where these changes take place.
The whole issue is of course, performance. Different rules apply to different types of operation and aircraft.
Although absolutely vital in limiting situations, where it should have your complete utter and undivided attention to getting it right, most of the time it's regarded as being dull and boring, something that must be learned.
Hope this helps.