The fourth land is often a swinging point in a game and if either player misses that land drop the chances of them losing increase significantly for most decks
Of course, if you're putting it in your deck, it means you've taken that into account and are probably running it in decks that look to Donate it to opponents with cards like Zedruu the Greathearted, Stiltzkin, Moogle Merchant, and Iroh, Tea Master
Because you can just fill your deck with big booty Creatures, you can win a game in an instant by playing Phenax and then just tapping everything
Give some of these a chance
Halo Fountain isn't necessary to win the game, and it acts as a solid "plan B" to the primary win condition of winning through traditional combat means
Hes especially fun in decks that love sacrificing or reanimating creatures