The chunking behaviour is transparent unless you have a side-effect in your sequence function, which isn't sensible anyway. The chunked behaviour performs significantly better for the majority of cases which is why it's on by default, I believe.

Rich (creator of Clojure) addressed concerns similar to yours in this reddit discussion:

http://www.reddit.com/r/programming/comments/afyav/clojure_1...

He also discusses chunked sequences in a video here (near the bottom of the list, the sound is pretty bad):

http://tomfaulhaber.blip.tv/

Rich hickey heard you

http://clojure-log.n01se.net/date/2010-01-22.html#15:01