A 6/6 flyer is already a threat, but the moment it hits a player, it can wipe their entire creature board and clear the way for your next attacks
This, in part, helps reveal the power of commanders such as Thrasios, Triton Hero and Tymna, the Weaver, rather than being combo pieces they are simply value commanders, and thus blowing them up only prevents one opponent from generating value (though Thrasios is often used to draw an entire deck) but with a win con as elegant as "exile your library" coming out of black, and "win when you draw with no deck" coming out of blue at extremely low mana costs, it really enables you to play the T&T combo that makes them far and away the most common cEDH commanders
Indestructible equipment will not be destroyed if targeted with a removal spell, unlike other equipment cards that would be destroyed and placed into the graveyard
This is incredibly useful in decks with a lot of different upkeep triggers that want to double the value being generated by those triggers