good website does not need a sitemap.xml work on your website quality and you will be rewarded. One of my websites has only pr2 but it is indexed in 1-5mins after i publish new article!
If you have pages 5-6 clicks away from the main page, I think that Google SiteMaps will help. But Google SiteMaps also has the role of a stats program regarding the relation between your website pages and Google Search Index & Bots.
I found it helps index my page quicker. It can´t do any harm anyway and only does not take too long to create.