Now, because you could immediately pay a seven-fold of life for an equal amount of cards without anything else, Griselbrand was immediately impactful, and has been ban-hammered in Commander
[1] Later on, the player can build decks with the cards to battle against other players
Teaching games - small streamlined decks tend to focus on one strategy, and use a few specific tactics, mechanics, to get there - a larger and more unfocused deck can be used to teach new players broader groups of mechanics and the way they interact better than competitive decks can
Good luck and have fun
For deck testing, the set is especially useful when comparing mana bases or testing whether a deck needs stronger fixing before buying or moving around official copies
Bonus remark: You can play Kaheera, the Orphanguard in a Vadrok EDH deck, but not the other way around