Google Says:
The robots meta tag lets you utilize a granular, page-specific approach to controlling how an individual page should be indexed and served to users in search results. The directives specified using the robots meta tag are used by Google for crawling and indexing the pages and the links on that particular page.
Several other directives can be used to control indexing and crawling. Each value represents a specific directive. The following table shows all the directives that Google honors and their meaning.
The nofollow meta tag <meta name="robots" content="nofollow"> clearly specifies that the if the header of the page has this tag then, Googlebot should not follow the links on the page.
But, the recent announcement by Google introducing the sponsored, nofollow and ugc attributes to be used as rel value in links and has changed the meta tag nofollow from a directive to a hint.
This was clearly stated by Gary Illyes in his tweet :
1. There's no meta robots ugc and sponsored, it won't do anything if you add that.
2. Meta robots nofollow is a hint now, like rel-nofollow.
3. I'll update the docs tonight to say this explicitly.— Gary "鯨理" Illyes (@methode) September 12, 2019
What is the difference between a directive and a hint?
A directive is a direct specification on which the mentioned action has to be taken by the bots. Hence, earlier when the page had a nofollow meta tag in the header the bot completely ignored the links on that page. A hint means that Google may or may not obey the Meta Robots Nofollow when it encounters it.
The reason for this is given by John Mueller as a part of the Twitter conversation is as follows:
The meta tags are specified at the page level and the rel values are specified for each link. The logic behind the nofollow meta tag becoming a hint rather than a directive is that using <meta name="robots" content="nofollow"> is like using a rel-nofollow to all the links on the page from now on.
One thing that we need to be very clear about is that there are no meta tags for ugc and sponsored. Adding that will just pollute the code with unwanted lines of code.
