I wouldn't do it. In most dogs, especially Labs, the dewclaws have bone in them that is extremely painful to remove.
Some dogs, like Great Pyrenees, for example, have multiple dewclaws and some of them are attached only by a flap of skin. Those ones are sometimes removed at the same time as neuter/spay since they are most likely to get caught on something and injure the dog.
As others have already said, YOU don't remove them. It's done by the breeder before 3 days (that's our vet's preference) and if you happen to get a dog with them, you leave them on.
At this point, with having a dog that has them, there are really no negatives as a pet owner other than you will have to make sure that nail stays cut short as it doesn't wear down naturally. The positives are that dogs actually use that toe for gripping bones and such.