The document discusses different types of site structures in Microsoft SharePoint - deep versus wide structures. A deep structure uses top-level sites with many subsites, while a wide structure uses fewer top-level sites without subsites. Explicit site collections work best with deep structures and allow over 250,000 subsites, while wildcard site collections are better suited for wide structures but are more limited in the number of top-level sites and subsites. The document also provides guidelines for the maximum number of site collections and subsites depending on the structure type.