Since only black mana can be used for Crypt Rats, it's often played in decks that primarily use black mana, as the more colors you add, the harder it can be to activate
if you assume, on average, you're drafting 31 playables for your deck (23 spells, 5 lands, 3 sideboard cards) then approximately 10% of your cube could potentially be strong sideboard cards and the resulting decks would be 'more powerful' than a cube with no sideboard cards
DJ Johnson: I love the black and green color combination
It was largely designed to make mulligans less painful in Standard and Limited
A handful of the best ways are Virtue of Loyalty, Chivalric Alliance, Forth Eorlingas!, Court of Embereth, and History of Benalia