I remember trying to compare these before (but not what I ended up thinking), so maybe it's better if I just explain what it does:

When you change your "context", all of your open apps and their windows (on all spaces, on all screens) are closed. The apps and their windows from the context you are switching to open – their positions and working state recalled from when you were last in this context.

You can only be in one context at a time; Think of it as a workspace or project manager in an IDE, but on the OS-level.