Is Sitemap XML helpful for indexing and caching?

[Jack London]

I don't know why I think sitemap xml is not helpful more in SEO
For example: I have a new website and I submit sitemap xml to google webmaster tool, also submit URL to google crawl site but seem Google indexed my site slowly, just 6 pages indexed and homepage was not cached at this time. Perhaps, I need to make link exchange for it on high quality site for get fast index and caching my site.

what's about you ? what do you think about xml sitemap, It's helpful to you ? or not. please show me some benefits if we submit xml sitemap to Google webmaster tool

Thanks in advanced!