Sewing large panels of fabric is deceivingly difficult. Fabric on a sewing machine does not behave like wood on a table saw, even with heavy spray starch. Making 90 degree angles at every corner requires a lot of layout space, accurate measurements, and knowledge of the textile properties and machine capabilities.
Modularizing components, like in quilting, is one way to manage working with large panels. Modularizing also adds an intimate scale to a project and visual variety.