We rarely worry about that creature weve just given them either
It also doubles as a nice decorative statuette when you are not busy demolishing your opponents with 10.000 needles
In a deck where the commander requires targeting with instants and sorceries to add power, toughness, and bodies, finding ways to grant those bodies evasion, present additional power, break board stalls, and reduce the risk of retribution is key to winning
Norn is expensive and has a huge presence on the board, so better protect it as best you can
Destroying them turns them into a land which can transform back into the creature side for paying 3 mana and meeting a small condition
It lets you draw a card and proliferate which means you are able to add an additional counter to any creatures you control that already have a counter on them