Many people do not cut their hair for long periods of time, even years. If you have really great hair genes then this may not be an issue for you. But for most people this will either cause split ends which will cause the hair to break and you will have a hard time growing it longer, or it will get long but very frizzy and be very dull and dry.
Having regular hair cuts are important when trying to grow out your hair to prevent dead ends and to prevent the ends of your hair from becoming too damaged. Even getting it cut every 6 months is okay unless you spend a lot of time swimming or in the sun which increases hair damage.