How do you know for sure if it is knitting in the round or not with circular needles?
There are instances when the circ ndls are used to work flat because of their length (ie the width of an afghan) where straights are too short. Or you might work the body of a pullover on circs...ITR...but then go to working flat once you get to the armholes. Normally there's no seaming when truly working ITR.
Using dpns is when the circumference is too small to allow for circ ndls (altho you have the option to do a form of Magic Loop). I opt for dpns when down to fewer sts. Feels more manageable.
A hat can be worked with circs and dpns...no seams...start to finish.