There is a stitch where you purl into the back of a loop. It does twist it, and thus makes it tighter. I've never heard of anyone doing it randomly, but then again, I'm big on following directions. It's also not something exclusive to knitting in the round.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry