Interesting enough…I have always been the proponent of relevance matters. Way back when because it will shortly matter as Google makes the changes, but according to this Moz blog post, no one has been able to prove the concept (6 Changes We Always Thought Google Would Make to SEO that They Haven't Yet - Whiteboard Friday - Moz) excerpt provided below:
So number one, a lot of people in the SEO field, and even outside the field, think that it must be the case that if links really matter for SEO, then on-topic links matter more than off-topic links. So, for example, if I'm linking to two websites here about gardening resources, A and B, both about gardening resources, and one of those comes from a botany site and the other one comes from a site about mobile gaming, well, all other things being true, it must be that the one about botany is going to provide a stronger link. That's just got to be the case.
And yet, we cannot seem to prove this. There doesn't seem to be data behind it or to support it. Anyone who's analyzed this problem in-depth, which a number of SEOs have over the years -- a lot of people, who are very advanced, have gone through the process of classifying links and all this kind of stuff -- seem to come to the same conclusion, which is Google seems to really think about links in a more subject/context agnostic perspective.
While I still believe it is the best practice, I must add that as recently as a week ago I commented on a thread here in adamant support of the concept in contradistinction to the majority of people in the thread.