When you place two dissimiliar metals in a conductive solution (ie potable water) a small current will flow. The anode will rust (be consumed) while the cathode is not. A steel WH uses aluminum, zinc, or magnesium anode rods which are designed to be consumed over time so the steel tank doesn’t rust. Once the anode is largely consumed, the tank will begin to rust. This website encourages people to monitor and change anodes so the tank remains protected. An engine which has regular oil changes lasts a long time. Don’t change oil and the engine quits. Don’t change anodes and the WH quits.
Of course removing an anode and not having one at all will most certainly void warranties. As a no anode WH will probably fail in a couple of years, the plumber gets extra business to put you in another one. The powered anode should not be consumed as you are actually driving current rather than relying on passive galvanic current from dissimiliar metals. Most gas stations with underground tanks now use powered anodes to prevent their underground tanks from rusting.