The advantage of working with Google, rather than againts, is all the statistics they then can give you back, like how many pages they have indexed, if they can't find any pages, how often they crawl your site, what keywords was used to find your site.

It's also very helpful to help you track any improvements as the result of chnages etc. The more you give Google, the more you get back, so i would always recommend submitting a sitemap, no matter how good you think your navigation is.