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

Different teams link and share their models during the design process because ultimately their projects will have to be merged/coordinated for the final model. The advantages of linking models is that you're allowed to look at/layer different project models so that models are accurate/centered. Also, this allows for each team to look at but not touch another's project, they are protected. The only disadvantage I found was that sometimes the linked project view would get in the way or make my project view too clutter, but that can easily be fixed changing visibility/graphic display options.

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

Before digital models, the main design method must have been to use pen and paper. I take it then that maybe each design group had an initial meeting to go over the general shape/structure of the project. From there each group worked on their concentration/focus and after a while met up to see how each team was progressing. There would probably be many check-ins throughout the project design. Finally, teams would probably have a last check in to see how each of their designs work together and identify potential problems. It probably was a lot more difficult to coordinate team projects before digital models existed.

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

After models are shared digitally, design teams can use them to link their projects to one another to see how the projects align/overlap. This can also be done more effectively if they upload and coordinate their projects, just as we did using the BIM360 tool. This will let them see how their projects interact and identify clashes. These clashes can then be resolved prior to construction