Hanging sections mount off of the wall with the use of a metal cabinet hanging system fastened to studs. This helps with cost due to less usage of material with shorter verticals and no bottom shelves.
Shelving & Drawer sections still mount off of the floor. The reason is due to the force of opening and closing drawers over time can weaken the system with possible failure.
Shelving sections can hold large amounts of storage with different types of weight so floor support is nesscesary
All sections mount from floor and attached at top with steel cabinet rail fastened to studs