Complex sentence: In general, butterflies are used only for very large materials (6 ft x 6 ft or greater), while smaller sizes are usually sewn on to portable frames (similar in construction to picture frames) for ease of placement and storage.
Split into simpler sentences: In general, butterflies are used only for very large materials (6 ft x 6 ft or greater). For smaller sizes, materials are instead usually sewn on to portable frames (similar in construction to picture frames) for ease of placement and storage.