Dewclaws are removed to help prevent the "hanging" accidents that often occur with dogs. They'll accidentally get the dewclaws torn in a lot of incidents. Some people don't, but it's considered safer. Dogs are especially prone to it if they're allowed to run loose in brush, etc.
All 4 of Barkly's dewclaws were removed--Vlad was back-only since a lot of big dogs use them to hold things to chew. Vlad's one of the first dogs I've seen that had any of his dewclaws since Daddy's white GSD Cindy, and the vet told me that if he tore one, we'd go ahead and remove them.
In a lot of cultures they don't do anything--they leave dewclaws; don't crop ears; don't dock tails--unless they tear one of them. People started doing all of those things when certain dogs started showing tendencies of getting those body parts injured--ears torn or infected, broken tails, etc. It's not just for looks the way a lot of people think--with dewclaw damage being something every dog breed has in common.
Scent hounds are one of the few I know of where people absolutely want long, floppy, infection-prone ears that can get ripped in briar patches. Most terriers would suffer broken tails because when they were rarely anything but working dogs, their owners would grab their tails to pull them out of vermin holes. A shorter "handle" was less likely to break. (I can't imagine pulling on any of my dogs tails for any reason though.) Since it's part of their spine, tail breaks can be REALLY painful affecting the whole body.
A lot of people have quit having ear and tail modifications now b/c they don't have actual working dogs, but generally dewclaws are removed no matter what.