An accordion's bellows are a fragile folded structure that wants to spring open under its own tension, and a full-size instrument can weigh 20 to 30 pounds concentrated in dense reed blocks. Strapping the bellows shut before it moves anywhere is the one step that protects the whole instrument.
Pro tip: If your accordion is older, check that internal reed wax has not softened after a hot move by testing a few notes in each register before a performance, since heat-softened wax can let a reed shift slightly out of tune.
Watch out: Never transport an accordion without the bellows straps engaged; the folded bellows are under spring tension and can pop open and crease or tear if left unsecured.