Look at it this way.. Light parties of 4, full parties of 8, raid groups of 24. 24 is about a big a group you can feasibly manage for raiding anymore. Take that light party to 5, now we have full parties of 10, raid groups of 30.. Getting 24 people together is going to be an effort in and of itself, bump that to 30, might as well be back in the days of 40 man raids that took half a day to organize.
