When I do Windows+S I see this effect.
How can I disable this?
Install CompizConfig Settings Manager (CCSM).
sudo apt-get install compizconfig-settings-manager
Click on the Ubuntu Button (in the top-left corner) and search for CompizConfig Settings Manager and open it.
There scroll down to Desktop section and look for Expo and click it. Click on the Expo key's key-binding and uncheck Enable. That will disable the expo feature. You could also alternatively assign a different key-binding to it.