With careful deck building, MDFCs increase both the number of lands in your deck (thereby preventing mana screw) and the number of spells in your deck (thereby preventing mana flood), which is incredibly powerful
If your deck is trying to cast as many X spells as possible every turn, and wants X to be as much as possible, we probably want to prioritize ramp more highly than just 8 or 10 spells - in fact, I can see running 60 mana sources, like this Vaevictis Asmadi, the Dire deck
The other white bear thats on everyones minds
Summer Bloom threw this rule out of the window by allowing its caster to play three additional lands in a single turn
The Blaine Supporter card is a key focus, as well as Ninetales, Rapidash, and Magmar, in order to make the most out of this card
It all works tightly for the mana package