Which types of structural framing systems and materials are most commonly used in the US for residences? For office buildings?

US residences typically use wood-framing for structures. Office or commercial buildings typically use metal stud framing (and possibly concrete/reinforced concrete.

Why do different teams of designers and subcontractors link and share their models during the design process? 

What are the advantages of linking models?

Are there any disadvantages to linking models?

How do you think design coordination was done before we started using digital models? 

Before digital models, design coordination required using pen and paper techniques to share models across disciplines, designers, and companies. Digital models have multiple advantages such as allowing collaboration without having to pass physical copies between parties, allowing design updates to be shared instantly, and checking for clashes in designs. All of these advantages make it easier to work collaboratively and save time.

What strategies can design teams use to find and avoid clashes prior to the start of construction? 

Working collaboratively with digital models allows various design teams to monitor each other's work and communicate about potential clashes as buildings are being designed. Aside from the ability to easily share digital models, many software programs for digital design have systems in place to check for potential clashes, which adds an additional layer of "checks" to minimize the amount of clashes during construction.

At what point in the project development process should design coordination start? 

Is it ever too early?