I think,
it depends on the context of the situation, which most of the time its how much cardio is done, the frequency and volume being done.

The benefit of cardio would be any form of exercise/activity that is designed to work the cardiovascular system and increase in circulation of blood and oxygen throughout the body. Getting your body to sweat also helps you to release toxins from the body. The benefits range not only with weight loss, improved Heart health, improved stamina, improved immunity, stabilized blood pressure, increased energy levels.

The two main questions would be

  • Is cardiovascular exercise the only form of training the individual does?
  • How frequent is the cardiovascular work being done?
  • How is the nutrition of the individual?

You don't lose muscle from running, but your body will direct resources to the muscles being used, and the developing muscle will be aerobic muscle. I often put on a pound or two of muscle when I start running more as my legs and core build up. Hypertrophy happens with running as well as any other activity.