The obvious: it prevents damage to everything in the package. If you're checking a bag, you don't have to worry about other suitcases piling up on it and destroying any dangerous items you've packed. As for your carry-on luggage, you don't have to worry about it dangling around or maybe even getting squashed by other items in the overhead bin.

Safety: Harder-sided luggage is harder for thieves to get into.

Waterproof: You don't have to worry about turning it in heavy rain. If you land and walk 10 minutes during the rainy season, your suitcase may be dripping when you arrive at the hotel, but you will open it and find a nice dry suit to put on.

EASY TO CLEAN: Hard luggage case no need to worry about someone spilling coffee on your suitcase, or pushing it through a muddy puddle. Take a damp cloth to the spot and it will clean in no time.