They were put in to stop dispel spamming and if there is a dispel shield they have to use a dispel to take one of the dispel shields off. They can only cast a dispel when there is no dispel shields
Dispels shields are considered protection from constant spamming on dispels back to back on the opponent like it was in the pass. Which pretty much stalled out match and preventing the inevitable for short time sometimes even switching to flow of battle. Soon or later we might even get a same type spell spam spell shield to prevent spams who knows.
