Glazing bars for polycarbonate sheets are used to join and secure the sheeting down to your frame. Primarily, they are essential to ensuring a strong installation that is resistant to wind uplift and rain loading. The secondary use is to create a waterproof seal between the sheets to make the roof watertight and avoid any leaks. This is done via the rubber gaskets and clamping pressure.
Self supporting glazing bars join polycarbonate sheets the same way but avoid the need for a timber or metal structure below the bars. These are most commonly used on car ports, pergolas and canopies.