It saves you the most money in the long run, heres a quick calculation: At 750 gems : $0.00675 per gem ($4.99 / 750) At 20,000 gems : $0.00499 per gem ($99.99 / 20,000) At 40,000 gems : $0.00499 per gem ($199.99 / 40,000) If you buy the 20,000 pack, you save (20,000 / 750) x $4.99 $99.99 = a little over $33
If you have ways to gain a lot of life early on, you can pay a ton of life to get your whole deck into your hand winning the game with all your win conditions in your hand when your turn comes.
Explainer videos that turn complex ideas into clear decisions
You usually Planeswalk away well before anyone gains any quality amount of life, and then the potential card drawing only gets better for others until you walk away
You can also purchase fully assembled competitive tier decks, such as the top decks from the most recent Magic World Championships shown below