The short answer is yes, but not much. Windows Defender is a definitions-based system, whereas WSA works on a cloud-based classification model. The benefit gained by running both is that you are layering your protection. WSA allows for this by running properly alongside other AV solutions. That said, instances in which Windows Defender catches something WSA doesn't are exceedingly rare. There's no good reason I can think of not to just go ahead and run both though.

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"... WSA allows for this by running properly alongside other AV solutions... " this is true only for windows up to windows7.

If your version is 8 and greater only one AV solution, one AM and one FW can be registered and be active. (wiki article on answers.microsoft.com).

If you install webroot on windows8 the WD will be deactivated - no chance to activate both.

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