The main reason I would put forward is that it's completely free and open source. That means that all your work is transferable and usable by anybody, not just people who have the ability to use Matlab (including possibly your future self).
I must admit, that sounds plausible and I'm not an expert with Matlab or Octave, but I understand the compatibility is reasonable but nowhere near complete. There seem to be a pretty good number of problems discussed here:
But really I just feel like (certainly in my field) the open source community around R is huge and thriving and it's a better bet than Octave in terms of that.
