It is almost unheard of to build a new web site and not launch with a basic XML Sitemap for better search visibility.
But most experienced SEOs know that it is not really needed for all sites, especially smaller sites.
Today, we have Google backing that up in a Google Webmaster Help post.
Googler, John Mueller said:
With a site of that size, you don't really need a Sitemap file, we'll generally be able to crawl and index everything regardless.
Also, with such a small Sitemap file, you can just check the individual URLs to see if they're indexed like that.
John from Google is making two points here.
(1) Google should have no problem indexing a small web site without a sitemap, so it isn't necessary to spend the time making one.
(2) If you are using the Sitemap approach to check index count, that too is a bit worthless in that small sites are easy to check how many pages are indexed by just typing in the URL of the page into Google.
It doesn't mean a sitemap file for a small site is hurtful, it just means it is not required or necessary.
Forum discussion at Google Webmaster Help.