If you want your shelves to stay up you need these!
The 20" position shelf brackets are for use with the following:
20" (50.8cm) deep Linen or CloseMesh shelving.
The shelf support brackets are needed to support the shelf and therefore you would need one every 36" (91.4cm) along the shelf's length, and also one at each end if you are creating 'open ends' or floating shelves, where 1009 - shelf support poles, or 974/980 - wall brackets have not been used