The trick to big WC's is to be sure your new water is the similar to the old water with respect to temperature and pH... and of course has been treated with a good water conditioner. Smaller water changes are suggested most of the time because, for most hobbyists, it's hard to get this right. If you are pre-treating/testing your water before it enters the tank, you can do the big water changes regularly. It's much more dangerous if you're not doing this... i.e. you are sending water directly to the tank from the tap and adding water conditioner to the tank.