So a friend of mine recently implored me to do this for SEO reasons. Since he quoted me, I will quote him in turn:

if we backlink each other
we get SEO++

Fortunately, while he has to maintain a veneer of professionalism on his site due to his grad school applications (if you’re reading this and you are evaluating his applications, he’s a cool bloke, do recommend), I don’t.

Anyway, SEO++, index me more Mr Google (or bing or ddg).