They must be constructed to bring out and present the character in every way possible! Every piece has to be evaluated on many levels to serve its purpose. It must be done by a staff who is trained, seasoned, and passionate about the process.
Hours are spent choosing fabric, trim, notions, etc. and observing how it reflects light or how it absorbs light, is it heavy or is it lightweight, and understanding that sometimes it’s necessary to have both. In some cases, a heavy costume helps the actor “feel” their role and step into that character; even down to comfortable character shoes! It’s impossible to ask an actor to give everything they have on stage, meanwhile suffering because the shoes weren’t a priority.
Just as important, costumes need to accurately reflect the time period, the culture, the demographic and the character’s surroundings. To tell a story in its truest form, you must be able to give the audience a window into that time and place. It’s paramount to make sure that all those pieces are authentic. We go to great lengths to find materials that provide and instill relevancy.