With a countdown you have a definate idea about how long you have to wait but a progress bar is all about the perception and the relative amount which has to be done.

For example,taking the progress bar of installing windows as an example

![enter image description here][1]


I know there is quite a bit left but I can not be sure about how much time those 75 updates will take since it is dependent on so many parameters such as the time to install those updates,network speed,internet speed,processor speed etc.

Countdowns are more definite and clear about when the next action event would be

![enter image description here][2]


  [1]: https://i.sstatic.net/jwM0r.jpg
  [2]: https://i.sstatic.net/CXRK3.jpg