After added a simple fmt.Println in "for {select }" structure the cup usage is quite different , why? : Encounter a confused situation :  
let's say we have a "for { select }" function which is written in Golang.  
Here the code below:

    package main
    //import "fmt"
    func main(){

      for{
        select{

          default:
          _=1                     1. first situation 
          // fmt.Sprint("aa")     2. second situation 
              }
      }
    }

while in the first situation the cup usage shows below:
[![enter image description here][1]][1]
in the second situation the cpu usage shows below:
[![enter image description here][2]][2]

I guess something happend in fmt.Println .  
May be related to the mechanism of Golang fmt realization ?  
Not quite sure how it happens by using all the cpus ?  
Thanks in advance !

  [1]: https://i.stack.imgur.com/dw7jn.png
  [2]: https://i.stack.imgur.com/CB9CO.png