As the game expanded over the years more and more cards get added to the game. The sheer amount of information to keep track of is for many people overwhelming. With MemorizeHS you can train to get better at remembering Hearthstone cards.
I think there are a total of three reasons that are important:
First, it helps your deck building abilities, since you will find not-so-obvious synergies (Missile Launcher & Venomizer for 8 mana board wipe, or Meat Wagon and a magnetic card to "control" the recruiting of the deathrattle effect).
Second, it helps you with your actual gameplay (like the Meat Wagon example). It is also very important to know what removal options your opponent has at various mana costs to play around them.
Third: You landed here because you want to improve yourself. You can do this by repeating quizzes (through "Rote learning