I believe you are asking the wrong question. The better question is "What do you do to optimize your dress depending on lighting, weather and occasion?" For example, patterns washout in poorly lighted evening events where simple textured high contrast combos work best. Multi patterned combos work best in good lighting or during the day. Thus, I think the number of patterns used is the consequence of the goal rather than a goal in itself.
It seems that on SF, multi pattern matching is used as an exercise or as a method to demonstrate proficiency/"street cred".