Its all to do with the size of the aircraft and how it trims.
When i am doing load control for a flight getting it to trim with pax and bags is always a challenge. if you have a larger plane like a 737 etc its got more power and bigger holds so you can have heavier bags, but with a small plane (in my case a dash 8) they have small holds and are heavier at one end. They put a 20 K limit on it to try and 'purswuade' pax not to bring huge bags otherwise it puts the trim out on the small aircraft and you have to leave bags behind or kick pax off to get it to balance (pax kicked off is an extreme last resort by the way)
Hope thats some use, post a reply if ya need any more advice on the matter
