You'd think the robots.txt directive it pretty cut and dry. It hasn't changed much in the past several years, and it is one of the oldest directives in SEO history.
But Google's John Mueller devoted a whole one-hour long sessions on Google+ hangouts for just that topic and shockingly it lasted the whole hour.
Google spent one hour talking about the different ways to use robots.txt. Most of it comes from this help document but it is always nice to be given a live presentation on it.
John's presentation lasted about 25 minutes alone! Then the question and answer session took another 35 minutes or so. So even the most basics of basics, can be dug into in detail.
Listening to some of the questions asked, it does seem that even senior SEOs don't fully understand the differences between robots.txt and meta tags.
You can watch the whole thing here:
Forum discussion at Google+.
