im regards to porting a box, i think it depends on the displacement of the sub when in use (specs should be on the box or manual), some are designed for free air use, other arnt so porting can allow for a slight difference.
As far as i know, the weaker and smaller subs such as the 250Watt Kicker ive seen at Repco comes with a box which isnt ported (at least the one i saw) and i checked the specs of it and its displacement was quite small when compared to more upmarket subs like JL's which have much bigger displacement in comparison and come with ported boxes.
My 12" Pioneer isnt ported, it came with a professionally specified box for it and i guess a port wasnt needed. Im also wondering if porting it would have a noticible difference in SQ.
thats my understanding at least