They are removed to prevent them from getting caught and ripped.
In some herding breeds, the dogs actually use them for turning and they are left on...most retrievers and field dogs have them removed so they don't get caught. Personally, I would love to never clip another dew claw LOL
Don't some breed standards require the removal of the dew claw? Maltese doesn't. Our puppy has her dew claws. When I asked the vet, she said that they are different on different dogs. In malts the dew claw is "attached" and more like a regular digit or "finger/toe". If it is removed within the first few days, the connective structure of the claw hasn't completely formed. If you wait for later removal, it's like cutting off a finger or toe. She likened it to de-clawing a cat. Our puppy's dew claws do feel like her regular claws, they aren't floppy at all. I just make sure to trim them often. The nail on them is much thinner and easier to clip back. But you do have to make sure not to hit the quick, otherwise it will bleed and be painful...think about how your nails feel when they are clipped too short.
jellybn, it's that "fingernail" just between their elbow and foot. It's kinda like a thumb, of sorts. Your Malt might not have one. If you have access to another dog, touch its ankle area until you feel a nail sticking out.
I wish I could get Little C's removed. They are extremely curly and very difficult to cut. They are short short short, and yet, they are still practically growing into her legs. I can't cut them any shorter because of the quick. It actually DOES hurt her every time I cut them...it's hard to get a hold of them to clip them. Sir N's are curly, too, but they don't curl immediately like Little C's do, so they are easy to cut.