For a practical example, why would you play a card like Llanowar Dead when you could play Birds of Paradise instead
But the Ninth Doctors is perhaps the most offbeat
Put a +1/+1 counter on each of up to two Soldiers you control
The final bit of text reads: If a legendary permanent or an artifact entering or leaving the battlefield causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time. Basically, Gandalf the White can do a lot of good stuff, and being a 4/5 isnt bad either
Coststorm (When you cast this spell, copy it for each different mana value among other spells and lands you've played this turn.) The copies of Friarball created by its coststorm ability are put directly onto the stack
Im not terribly high on it because its just another aggro +1/+1 counters commander at the end of the day, but I get why others might run it