I bought a second 35mm body when I began to be asked to do paid commercial work again. Early on I assisted a pro and shot some of his non-studio jobs, having access to all his kit. Walking around with a single camera body for my personal work was a delight in comparison. It was some years after leaving regular commercial photography that I was asked to shoot 35mm for money - I'd always done a little medium format work - and having back up is essential. Add to that a mistrust of plastic bodied cameras that were coming into vogue. Other than commercially I've never felt under gunned with a single camera and lens.