It's not so much necessary as it is more a convenience. We're able to carry six of them at a time with us when we travel.

My boyfriend's only got two of them, though, and they usually wander around freely.

[ Yours are bigger, Daphnes! That is impressive! But we all know bigger doesn't always mean better-- no, Unfezant, don't turn this into a competition! He's ruffling his feathers again. ]