Rapidbot and/or Sitemap Plus and/or native Sitemap

I’ve been using Sitemap Plus for some time but also have Rapidbot lying idle in the add ons folder. Does Rapidbot do anything that Sitemap Plus doesn’t - in other words, is there any point setting up Rapidbot?
And when it comes to submitting a search engine sitemap, is there any advantage to doing it through Sitemap Plus rather than the native Sitemap in RW.