This makes it easier to create prototypes.
This is a demonstration of how Bootstrap can make our lives easier. We don't have to spend a lot of time doing boilerplate/grunt css work to get our instructional design ideas up as prototypes.
In Bootstrap, classes are very important. Make sure you are very mindful of classes.
In Bootstrap, the hierarchy of classes to build more complex "parts" or components is important. Be mindful of what specific classes are being utilized as a parent > child > child-of-child.
In Bootstrap, the class names are arbitrary in the sense that they are no different than class names you would come up with. Each class is assigned to a particular set of CSS rules. In studying, it's important that you get a "gist" of what the classes you are applying are actually doing.