The most obvious and frequently used argument for playing the minimum number of cards is simple: some cards are better than others, some cards will be your best cards, and you dont want to reduce the frequency with which you draw those cards
Edgar Markov Edgar Markov is the go-to vampire Commander, with the certainly-broken Eminence ability (shared by another one of MTGs best commanders who just missed out on the list, The Ur-Dragon), allowing it to generate endless vampire tokens without ever even being cast and in a way that cant be interacted with
The media giants playing both sides of the field
Friendly to a card type This can involve a wide range of things where you either help that card type (making it cheaper to cast, enhancing it in some way, using it to generate an effect, etc.) or that card type helps you (you get rewarded for playing that card type, having a certain number on the battlefield or in your hand or in the graveyard grants abilities, you can sacrifice them as a resource, etc.) Friendly to artifacts Primary: White and blue Secondary: Red White and blue, as the colors of civilization, are both very friendly with artifacts
With Amazing Spider-Man, they play a key role in paying for the web-slinging cost