It depends on your outdoor cooking style. If you are going to cook from scratch, you will probably need more than one pan and a cookset will keep the bulk down as the pieces will all nest together.
I take only a titanium pot, a titanium mug and 2 Lexan teaspoons for backpacking as that suits my cooking style (home-dehydrated meals) and keeps my pack weight down. It's also more versatile than you would think.
I do, however, use an MSR Blacklight cookset for car camping. The drawback with cooksets is that, often, not all the bits are equally useful. I have a Vango set that includes 2 ridiculously small cups, for instance. My MSR set has 2 good pots but the frying pan is a bit on the small side so I've added a Primus frying pan, which is excellent. I've also added a Primus kettle, which is surprisingly useful if weight is not an issue.
If you're buying for backpacking, think carefully before getting a cookset as you probably won't use all of it, which means that you're just lugging dead weight.