"All dogs need grooming; even little hairless dogs need special attention to prevent their skin getting dry. Very short haired breeds such as Whippets can get very greasy and smelly without the occasional rub down or brush and they need regular nail trimming or they can get problems with their feet. Double coated dogs such as Labradors need the undercoat removing, which if they swim and get rubbed down may do it but I have seen a few completely matted ones.
When you get your dog you should find out what grooming is required for its coat type, maybe as a groomer I see the worst cases of neglect but in my 25 years of grooming I have seen dogs with fleas and lice, maggots in their beards, a dog with its back legs matted together so that it could not cock a leg and similar in a bitch with terrible urine burns and several dogs who have had to be literally shaved to remove whole matted coats which is very painful for the dog often causing sore skin and then leaving them prone to sun burn.
A dog’s coat is there for a reason; it protects them from the cold in winter and has a water resistant top coat leaving the undercoat and skin warm and dry. In summer it protects them from the sun and keeps the skin cool by trapping air in the coat. I believe it is total laziness by owners who allow their dogs to get matted then shave them in the summer; it seems to be a modern trend to cut the backs of dogs as close as possible. The hair on the back will only grow to one length and then would moult and a nice new coat grow, by clipping it you prevent this moult and choke up the new coat causing the undercoat to grow through. This is then not water resistant or the correct colour or shine and offers no protection from the elements. The feathers are the bits that can get knotted but even cutting these will make them grow thicker but it is often good to cut the feathers around the feet and hocks for cleanliness and also to prevent painful knots between the toes and pads.
The exceptions to this is Poodles, Poodle cross and Puli type or Spanish and Portuguese water dogs, they have a coat which keeps growing and needs to be clipped regularly or left with the long coat which requires a good deal of attention.
The early Labradoodles either had the Labrador moulting coat or the Poodle coat, most of the second generation have the poodle coat which requires 6 to 8 weekly clipping and if the Labrador coat type ones are clipped then they have to be kept clipped.
Retrievers, Collies, German Shepherds and Spaniels have a double coat which should not be clipped. If they were, the coat would be ruined as explained above and could be grown out again but may take a year or would have to be constantly clipped and could grow thicker each time. In a heat wave I have occasionally clipped the stomach area of very heavy coated breeds such as a Newfoundlands so that they can lie on a cold floor but it is just as effective to hose them down. The coat grows back thicker as explained.