After reading various article on water heaters, I have a better idea how it works. The role of the Anode rod is suppose to be sacrificial. It rust instead of the tank.

Then it's logical to replace the rod every couple of years to extend the life of the tank. I was wondering if this is something that can be done by someone who's good with mechanical stuff but has no experience in plumbing. Most articles seemed to indicate that it is difficult because either there is no clearance or the rod gets stuck due to build up.