Are you talking about a sitemap in XML format that you provide so search bots can find every nook and crany of your site? I do support the use of those. If Google provides documentation on using and creating them, I’m sure its for a good reason and they should be used when possible. Especially on pages with lots and lots of content. For the blog portion of this site, I use a WordPress plugin that does it automatically for me, which is awesome.
And then there are traditional site maps which are just pages on a site that list every page on the site for saavy or curious visitors to drill down right where they need to get quickly. This is tricky territory, as a page with that many links on it can look awfully intimidating and be counter-productive.