If it's 7 or 8, two monsters are required, and 9 or above requires THREE monsters
[1] You can banish this card from your hand or field
Since a deck is limited to only four copies of a non land card usually, this added diversity comes at the cost of significantly reducing the chances of getting a certain card in a given game
TCG is one of the oldest mechanics introduced to the game
In addition, this process can become quite entertaining, and you may get carried away with it
Plus, running blue creatures specifically for sacrificing isnt the best strategy, since many blue creatures in competitive formats are value engines you want to stick to the board, or important combo pieces like Thassa's Oracle