@dlowan,
Probably because luggage is so restricted on flights these days so you often need lots of time to figure out what you can take.
My travelling companion is restricted to one 20 kilo suitcase.
Because I am going to the USA (odd) I can take two 23 kilo cases!!!! So it's not so critical for me.
I can take them from Adelaide to London....I can't take them from Berlin back to London!!
But I CAN take them from London to the US and back to Oz.
Luckily we have friends we can leave stuff at in England.
I am likely to be paying excess baggage when I fly internally in the US though, so I will still try to keep stuff to a minimum.