Having more than one way to win can make your deck more reliable (that is my opinion, it may not be true)
Once we had Priest of Titania creatures, it seemed natural to have Priest of Titania spells: (Wirewood Pride, for example was called "Giant Growth of Titania" in design.) The one-shot spells then led to permanents that trigger a tribal effect: Its interesting to note that Elvish Guidance got created because we wanted to find some way to get the Priest of Titanias effect into the set
Bant (green/white/blue) is the best color for drawing cards, and Deep Clue Sea takes advantage of the various support cards released over the years
[11] When old mechanics were revisited in the Time Spiral block, banding was left out for this same reason
In design, we call this a "brain freeze." You see, there is a line where you overload the players so much that they are incapable of mentally processing enough to function
This ability can really hamper the early games plans of anyone or a number of players use of mana rocks, and even though they get to choose, I still think this is better than getting three squirrels