Picture a person walking down the street pulling a bundle buggy or a wheeled suitcase behind them.
The buggy/suitcase isn't directly behind them, it's off to the side, on the side of the hand they're using to pull it. (Look at the people pictured here.)
This is inconvenient in crowded pedestrian areas, because your buggy takes at least half a "lane", if not a whole lane, so it's harder for people to pass you. It's also harder for you to pass others, because you take up more than a lane of space so you need more passing room. I've also noticed that, in a crowded grocery store with narrow aisles (**cough cough METRO cough**), something about the way it corners causes bottlenecks when the user is turning in or out of an aisle.
Solution: design buggies and luggage so that they follow directly behind the user's when the user is walking. Off the top of my head, the best idea I have is that the handle should be shaped like a J, L or sideways Z (but with right angles rather than acute angles). So the part of the handle you grip is at the side of the suitcase rather than in the centre (thus enabling the suitcase to follow directly behind you), but there's some kind of framework/architecture to cause the force to be exerted from the centre of the suitcase or from the whole front of the suitcase evenly, so that it will roll straight.
This would make users of wheeled luggage and bundle buggies less annoying to their fellow pedestrians and make life easier for everyone.