In general, letting your dog on the furniture is not going to cause problems - behavioral or otherwise. Dogs love to curl up on the sofa, the bed, and anywhere else that's nice and soft. They also like to spend time in their humans' favorite spots. Ultimately, it is up to you to decide the rules of your household and stand firm.
Behavioral EffectsAllowing dogs on the furniture will not necessarily make them believe they are in charge. It will not suddenly cause aggression or dominance. However, if you inadvertently reinforce certain behaviors, you will be sending the wrong message. Any dog that growls or snaps at you when you try to sit down should be removed from the furniture. If your dog refuses to move when you approach, he should be removed. Finally, if your dog "hogs" the bed or sofa, leaving no room for you, he should be removed. Making the furniture off-limits can be a temporary or permanent arrangement, depending on your preference.
Health and Safety ConcernsMany owners prefer to keep their dogs off the furniture because of the mess (e.g., hair, dirt and debris). Taking this a step further, some people are concerned about the potential for the spread of disease. There are a handful of diseases that are considered zoonotic, meaning they can be transmitted to humans from animals. A few examples include Rabies, parasitic infections, fungal infections and even plague. However, if you keep your dog healthy, the risk is very minimal. Whether you allow your dog on the furniture or not, all dogs should visit the vet every 6-12 months for an overall wellness check-up. A dog that has been vaccinated, is kept free of fleas, and is regularly checked and/or treated for parasites poses very little threat. You can minimize the amount of outdoor germs and debris your dog brings in the house by wiping the paws, spot-cleaning as needed, and occasional bathing.
Keeping Your Dog Off the Furniture
To keep your dog from getting on furniture, some basic training is necessary. Begin by teaching your dog the off command. Next, he should be taught the go to your place command. If your dog tries to jump on the bed or sofa, simply say "off" followed by "go to your place". Reward him when he complies. It is equally important to be sure your dog does not have access to the furniture while you are away. This is where crate training becomes helpful. While you are gone, keep your dog in the crate or confined in a small room away from the forbidden furniture.
After successful training, you may choose to conditionally allow your dog on the bed or couch. However, he will need to earn it. After all, it is a privilege - not a right. Before jumping on the furniture, your dog should be made to sit. Once he has obeyed one or more commands of your choosing, you can pat the couch or bed, allowing him up. If he oversteps the boundaries, he will need to get off the furniture. You must be consistent for this to be affective, otherwise, your dog cannot understand what you are asking of him.
Some owners prefer to keep their dogs off the furniture as a household rule. This might be for the purpose of cleanliness, to prevent damage, or for other reasons. As long as he has his own spot, he will be just fine. Be sure everyone in the household understands and enforces the rules. Inconsistency will confuse your dog and make the training process very difficult.