Sudden power, higher resistance to internal injury(shaking of the insides) vital target strikes, ability to protect body at a faster pace. When you can control your air and muscles, you can protect throat, temples, back of neck etc... Sorry for the incomplete sentences.
But there are garbage chi gong instructors out there. I went to a golden bell seminar and it was terrible. No martial application and the breath control was weak. They made it look so new age. They had me punch one of their better guys. Please note I don't consider myself powerful yet, well at least compared to my Sifu. All I did was a rooted relaxed swing(no power) and the guy's air got knocked out. The second time he flew back and the third time he just jumped out of the way. Then they were showing floor tile breaking with their heads. I asked why they keep their mouths open and not closed with the tongue up on the pallet they explained to me how bones are an excellent conduit for chi. I'm not an internal expert but that sounds fishy. $150+ a month!