I own and operate a quantitative finance business. Pandas (+ numpy) has been a godsend. Not only do I not have to pay for matlab licenses, but even the less experience programmers on my team have been insanely productive.
In my opinion, matlab's excellent object inspection and debugging capabilities can be replaced with strict testing standards in your code-base.
On top of that, I get to use a whole slew of libraries that are non mathematically related -- frameworks for web services, accessing ftp servers, sending e-mails -- a lot of automated "utility" stuff.
And it is all "free". Fantastic.
but the main one for me, was that python does non-math things much better than matlab. Since python is a general purpose language you can go from analysis to production application much faster, whereas with matlab it usually involved getting a software developer to rewrite it in java.
We used to take our python analysis code, wrap it up in a web app, and then use that to server risk information to traders, and it was quite easy to do so.