These inflatable pump wedge bags are often used by auto body shops behind dented door panels, or other applications where a shim with controlled expansion can be useful.
Recently, technician David Abdalian shared a brilliant application for piano technicians, which is to support a pedal lyre from below, either to keep pressure on newly glued repairs, or simply as a third hand to hold the lyre in place while reattaching, so it's easier to insert the hardware and braces.
The hand pump inflates the flat 6" square bag to about 3" tall. To deflate, simply press the button on the pump to release the air.