Did anything practically useful ever come out from the field of pragmatics so far?

Practically useful? How… gauche.

I mean, I love the fact that Implicature explains so much about language change and information transmission; Speech Acts are a great framework for making sense of how language is used to influence people; and Gricean maxims undergird so much of how humour works. But practical?

The closest I can think of (and it is, in fact, pretty practical) is pragmatics as the theoretical underpinnings for much of our understanding of cross-cultural communication, by giving us a way of making sense of how and why different cultures communicate differently. Politeness theory in particular, which is at the interface of pragmatics and anthropology, really helps you intellectually to not find other cultures swinish.