How Do You Choose Between A Simple And Complex Silo Structure For A Website?

In episode 188 of Semantic Mastery's weekly Hump Day Hangouts, one viewer asked about the considerations to make when choosing between a simple and complex silo structure for a website.
The exact question was:
In a video you once said that the simple silo structure would be sufficient for most sites. What determines whether you opt for simple structure vs complex? Thanks as always
