Many people just bundle up in their Gi in their gym / Gi bag. Then they pull it out for the next class and it looks like it was waded up in their bag. It comes out all wrinkled and smelly. Some don't use a bag at all. They simply crumple it up between uses.
It is essential to remove your Gi from your bag when you get home and unfold it. Then it must be hung to air out, minimizing microbial growth. You will be sent home if you come to class with a smelly Gi/uniform!!!
Properly folding your Gi and maintaining a neat and clean uniform is an indication of pride in oneself, your dojo, and the karate you practice. Assuming adults practice this habitually, it is important for children to learn this. And, hopefully it extends to other areas of their life, including folding their regular clothes at home.
Here is a short video showing the most common way to fold one's Gi / Uniform.