Bookshelves are usually at least 24" wide and up to 72" high if they are floor-length.
Cabinets are as small as 12" wide and 12" high but are typically much larger.
Many units can be installed next to or on top of each other to create additional storage.
However, keep in mind that storage that is too tall will be a challenge for shorter people to reach.
Large wall-mounted storage can also be visually overwhelming, especially if it is in a dark color.
Remember that deep wall-mounted storage could get in the way if it is installed near workspaces or appliances like top-loading washing machines. Be careful to install it somewhere where you or someone else won't hit their head on it.