Mostly, the reasons I chose to use multiple workspaces was for less visual clutter and more flexibility. Having all of the contexts in one GTD workspace was simply too much for me to look at, and overwhelm meant a higher probability of dropping the system, so I used the workspaces to visually compartmentalize. Also, using a workspace for each context allowed me to further sort them by adding labels — like specific projects that have a high importance (I am often working on multiple projects, both personally and as a freelancer and business owner). With a few labels I can sort my contexts quickly and this helps to prioritize next actions.
If you don’t need that extra flexibility, and are fine with simply sorting your GTD workspace by context, that should work fine for you.
Hope that was helpful! :D