1. There is a law of abundance - in order for the new to come, you must get rid of the old. Otherwise, for the new God, the Universe just doesn't see a place to "send" it to you.
2. There is a saying in China, "The old won't go away, the new won't come."
3. Old things are old life. By throwing out old unnecessary things, we psychologically set ourselves up for optimistic change and advancement.
4. Unwanted things, (especially if you have a lot of them) clog your life and your personality. Today you leave unnecessary things behind, tomorrow you'll stay at a job you don't need and spend time with people you're not interested in. Take from life what you need and make it quality in everything you do.
5. Holding on to things you don't need and thinking "maybe I won't have money for new things" sets you up for failure, poverty, and hopelessness. Set yourself up with confidence and tell yourself, "I'll buy myself a new one, I'll be fine, etc."
In life, in our actions, little things like this are just as important as big events. Choose a successful vector and don't let "the world of things" throw you off the right path.