Most points seem to have been covered. Geography isn't a degree like medicine or engineering where the skills are very specific to a particular career and, generally, doing that degree will lead to a fairly well paid job. But geography, as others have said, will equip you with a range of skills which will be useful in a range of careers. Geography, in my opinion at least, has better job prospects than English or history for example.
With regards to swapping to geog and econ, personally I wouldn't if I was you. It will make little (if any) difference to your employability (unless you're thinking of going into a finance related career in which case it might) and you'd be better off doing a course you enjoy. Also bare in mind that, as far as I'm aware, geog and econ at Sheffield doesn't have any physical geography in it and, given the fact that you've applied for the BSc, I can't imagine it suiting your interests very much.