Throughout your lessons at The Music Studio, you will hear time and time again from all of your teachers, that when you practice at home be sure to review/practice old pieces, as well as new ones.
The best way to explain why review is very important? SONGS ARE LIKE FRIENDS. Sure new friends come along from time to time, but it's important to check on the friends you've had for years. The friends you have kept longer, you know better and can build a deeper relationship with. As for your new friends, you are just getting to know them and can use your current friendships to build your new ones even further.
All in all, it's a good idea to keep those old pieces around. After all, they are all apart of the musician/person you are today (: