Sorry for the simple question, I've had a search, but I'm getting a million and one results

I'm curious about grow pots... I see that everyone is using polystyrene box's, and was wondering how they hold up? Do they break apart easy? How do they hold up in the heat?
I have a few large plastic pots that are large (probably 60cm diameter) and was just wondering if I could chop it in half (make it a bit shallower) and use that as a grow pot? or is the polystyrene used for another reason (other then it being cheap and easy)? The large, plastic, round pots seem like they'd work, but am not sure if they would be considered too deep?
I'm pretty tight for space, so am trying to figure the best way to get the most growth withouth putting them in the ground.
Thanks a heap
