When it comes to flexibility, wall shelves fall into two broad categories: modular and adjustable/removable.
Modular wall shelves offer versatile storage as you'll be able to add more shelves when the need arises. After a given time, you'll be able to create a whole wall of storage. When manufacturers develop their products, they consider the end use of the shelves, which means you'll find shelves that are capable of adapting according to your needs.
Adjustable or movable shelving is recommended for people who are looking for units that offer customization. This type will prove to be useful when you find something large like an artwork or massive book collection to showcase. With removable shelving, you can simply take out the shelves that are not needed to create more storage space.