We just adopted a healthy cat from the RSPCA. She was being fed Royal Canin at the kennels and I got a voucher for 2 free bags of the stuff, which she seems to like. However, it is really expensive, so I'm just wondering if it's worth buying this kind of premium food on a permanent basis? We can afford it and I certainly don't want to feed her rubbish as I wouldn't eat rubbish myself, but what is the real difference between this fancy stuff and the bog standard Whiskas, Felix, Gourmet whatever?