Honestly, I'm seeing so many people coming up with the arguments that the so and so winner of such and such a cup was unshod, and that certain disciplines seem to be abandoning shoes.
Personal opinion, it's not a valid argument.
It's like saying everyone should wear...let's say a jumper (top, sweater or whatever you call it where you live). Some people need it, some people don't.
Two perfect examples. My first pony and my friend's first pony. Mine didn't need shoes, and I trekked on roads, hunted, jumped competitively in all types of terrain (grass, sand, etc.) on him. He never went lame or had a problem. We tried to put shoes on him and he couldn't walk. Slipped and fell everywhere.
My friend's horse on the other hand, who was the exact same breed, similar confirmation, heck even the same colour even though that has nothing to do with it. Her mare was always shod. She did the exact same things I did. In contrast, she decided to leave her mare unshod, and guess what? Went ballistic. Freaked out at every new type of terrain. Could. Not. Walk.
So you see it depends on each individual horse. Some only need front shoes, some only need back. The reasons for getting your horse shod are also so varied it would take me the rest of my life to list them all. They could need extra grip if you ride on grass a lot and your horse tends to slip. The horse could have unsound feet and may need medically prescribed shoes to fix overgrown hooves, pain in the foot, lameness, etc. They could just have weak feet thanks to their gene pool.
So seek your farrier's and vet's advice, because they will through sheer experience, have a good opinion as to whether your horse needs to be shod. Don't listen to the claims that eventers are starting to abandon shoes, that winners of shows/vents are now more commonly unshod, etc. Simply because every single horse is different, and some just need shoes, while others don't.