Structural plywood is a better choice for applications that will be carrying a load, such as roof sheathing or flooring.
Non-structural plywood is a better choice for applications that will not be carrying a load, such as wall paneling or cabinet material.
Always consult a structural engineer to verify that the plywood you are using is adequate for your specific application.
Non-structural plywood is specifically engineered for interior use as paneling and cabinet material, as it will not carry structural loads like roofing and siding materials do. It can also be used as subfloor for underlayment in the installation of tiles and other non-load bearing applications such as wainscoting or chair rail. The (or plies) of non-structural plywood is very thin, usually around thick, and made of cross-laminated veneers. Non-structural plywood has no structural or load bearing properties, however it can also be used as subfloor underlayment for tile floors or other non-load bearing applications like wainscoting or chair rail. Non-structural plywood comes in sheets often solid core plywood.
Structural plywood is engineered to carry heavy loads, so it is commonly used with roofing materials and siding on homes and commercial buildings. Roof sheathing, for example, is commonly made of structural plywood because it needs to be able to hold the weight of shingles and snow. Structural plywood is also used in flooring, as subflooring underlayment and in boat construction. The plies of a structural plywood sheet are much thicker than those on non-structural sheets. This added thickness makes the plywood less likely to warp or bend when subjected to heavy loads.