In the process of stacking the bags up, baggage handlers have to grip both sides of your suitcase. To assist them, purchase suitcases with bar-type handles underneath. If you don't have enough handles on your bag, then the baggage handlers will have to grab wheels or other features to get a grip, resulting in those parts getting weakened, and increases the possibility of the handler losing his grip and dropping your luggage.
The process of unpacking luggage involves the baggage handler moving suitcases from the top of the heap to the their partner (or belt loader) who then transfers it to the ground - both process are most easily completed by dropping the bags. So, pack your luggage so that it can survive a fall of up to 1m.
Baggage handlers usually take better care of luggage marked "fragile", although it can still get dropped or bounced around.
Read this account by Carol Clifford & you'll understand why to make sure your bag has wheels:
Panic gripped me as I heard the loudspeakers at Brussels train station blare unintelligibly, and then watched all the passengers grab their bags and head for the stairs. NOT AGAIN!!! I grabbed futilely at a man’s coat as he rushed by me. “What did they say?” I spluttered. It was obvious really. This train was coming in on its original platform and I was going to have to lug my heavy bags – all 3 of them – up those stairs and down the other side again. But was I going to make it on time? Why couldn’t they have lifts or conveyer belts? And why, oh why, did my mother give me so many Christmas presents to deliver to the family? Huffing and puffing, my arms almost breaking from the weight of my large blue suitcase, I landed on the offending platform to see the train slowly pulling away. “WAIT!” I yelled, dropping my bags and waving wildly. To my great surprise the train stopped. Then I noticed the lady several metres ahead of me on the platform. Thanks to her the conductor had stopped the train and we were both able to clamber aboard. And that was how I learnt my first valuable lesson about travel: “Make sure your luggage has WHEELS!”
My daughter and I travelled together in 2011. We flew to Dubai, where we walked past 262 gates to buy a Starbucks coffee, before catching our connecting flight to London and meeting up with a friend. From there we eventually made our way a few weeks later via bus to Brussels, where we had to catch a train to Holland. The station didn’t feel any different from when I had been there 25 years before, but the experience was similar. We had to carry our suitcases, on wheels this time, upstairs to platform 9 where we would await a train which never came. This time the railway line was being worked on, and we ended up having to rush our bags down the stairs to try and catch a bus (which we missed) to the next station. We had to wait an hour for the next one, only to find that when we got to the next station, we were last off the bus and had to huff and puff our way over railway lines to get to the train which was about to leave. This one too, fortunately, waited for us to clamber aboard before it started moving. So the circle of life continues and it appears that things are not that different for this generation of travellers than it was for me all those years ago. But the wheels do help!