SharePoint server status "Installation Required" or "Upgrade Blocked"

I have noticed that servers in my SharePoint 2013 farm are showing statuses like "Installation Required" or "Upgrade Blocked". 

 When you install the SharePoint (CU) updates on one of SP server, we see the Installation required and upgrade blocked in the status of servers under the system settings in CA.

Installation Required : The server still not yet installed with the same CU that already installed in other servers in the farm.

Upgrade Blocked : The server is blocked from upgrade as they are on latest CU than other servers in the Farm. Current Server is installed with latest CU and it will remained blocked until all the other SP servers in the farm are installed with the same version.