Personally, I am a fan of having HTML Sitemaps – mostly for 404 like pages, so users who stumble on a page they are forbidden (sounds strict) to access, they have a way out but not out of your web site.

That being said, how necessary is it for Google and crawling? In todays day and age, Google does an excellent job finding content on web pages even if it is not linked to in a well-formed navigational structure. But HTML sitemaps can be handy in Google crawling your site naturally, not with an XML Sitemap.

The question came up in a Google+ hangout:

At the 5 minute mark John said:

But in this case, it is more important you listen to how John answered it versus just the words he used:

Forum discussion at Google+.