The benefit from domestic dogs can be enormous, but they should not be used for just anything that may be helpful to humans. Training them to find dynamite, drugs, use them as service dogs and similar, is dog abuse. Dogs must not be used as a mean to protect us, they should not be sacrificed or their mental stability destroyed.
Anyhow, there are segments in which they are not as burdened, and yet are much useful to us. This can happen only if the dog is properly brought up.
Some evolutionary theorists think that human survival had to do with the fact that dogs made us more efficient hunters. It is without a doubt that, throughout history, we had much benefit from domestic dogs. Their role changed, but first, they helped during hunting, guarded crops, livestock and entire household. There is a saying that one shepherd with a dog can do a better job than 20 shepherds without a dog. The guardian role stayed to these days. Dogs are beings with exceptional senses and can detect many changes better than us. Dogs' bark can be very useful because it protects us and warn us of danger, imposters, fire...
They are unbelievably capable to precisely tell if you are in a good mood or not, angry, under stress, anxious or happy. By watching your dog, you can very often spot your own problems that you did not notice before or that you denied.
Thanks to their body temperature, that is somewhat higher than human's – regular is 38.5 degrees – small dogs are used as mobile hot-water bottle for warming humans while they sleep.
Humans that occupy arctic areas of North America, Europe and Asia for thousands of years, would not be able to survive without Huskies and American Eskimo dogs.
Presence of dogs has positive effect on human psyche. They do not need much to be happy and that simplicity reminds us how we made our lives complicated and burdened. They will not love you less if you have smaller wage or lose your job. They teach us not to think about ageing, since they do not think about it but look forward to any given moment. There is no better cure for loneliness than a dog. Their presence lowers the blood pressure and relieves the tension. They make us be physically active. To go for a walk with them instead of watching TV.