If your dog is wounded, it is important to clean and then to disinfect the wound. This is for multiple reasons.
It is necessary to remove debris (such as grass, mud, rubble, dried blood, etc.) and sanitize the area in order to limit the risk of infection.
This also allows you to check the extent of the wound and the severity of the lesions. Indeed, it is not always easy to estimate the severity of a wound without cutting the hair around it, rinsing it etc… especially when it is well-hidden (between the fingers or in the armpit for example)!
Finally, washing and disinfecting a wound increases the chances of proper scarring and most importantly decreases the risks of complications. These could be of different types: delay in scarring, infection or a generalized sickness like tetanus.