More to let water in than anything else, though they need air to decompose properly as well.

A couple aren't really enough - I spike my bags all round.

Oops missed that Spritz. no a couple of holes is nothing like enough! Make lots...

That's the best bit - 'killing' the bag, MG!!! LOL.

I spike mine all over to keep the heat from building as they need cold to decompose (unlike a compost bin that needs heat). I dont do it for water as they are wet when they go in and hidden under bushes would get much water on them anyway.