As badbeard noted above, it kills my sinuses and gives me headaches also. But, sometimes if I am finding it hard to taste a blend, I will do it... with the possibility of much sneezing to follow.
Depends on the blend but I always retrohale some on every bowl. English blends I retrohale more and sweet Virginias...I think the retrohale is what made me fall in love with Virginias, burleys, orientals and even parique although I agree, you should take it easy with perique...I have given myself sneezing fits before.
Not often, if my palate is not detecting the flavor profile I will retrohale and my suspicions will either be confirmed that my palate needs some water or strong black coffee since whatever I had previous to lighting up is confusing the taste of my tobacco, if I don’t pick up,the nuance I expect though the tobacco has lost something so it will be set aside and mixed with other remnants.