Some pros: easy to lay, replaceable in patches in case of damage or spills, cost.
Some cons: usually used commercially, far smaller range of fabrics and colours, not usually advisable to fit over an underlay, many contain nylon (static build-up).
Another thing to bear in mind is that batches can vary, so if you're after a solid colour, you may find it difficult. Always good to have extras left over, if you ever need to fix a patch.
Fitting wall to wall carpet with underlay, gripper rods, stretching and all that it entails, is best left to people who know what they're doing, but another possibility is to look at something economic like a cord (ribbed) carpet that's hessian-backed, doesn't need stretching and just can be glued down over a flat rubber underlay... like Tretford Cord, if you can get it in the US or something similar.