There's a lot of confusion surrounding the actual benefits of optical centring.
What you quite often hear is people quoting that if it's not centred you're not using the best quality part of the lenses (i.e. the centre) and if you're a photographer and you like to read up on lens specs and optical quality of the centre of a lens as opposed to the corners that idea will make a lot of sense to you.
However the lenses in scopes don't work in quite the same way as they do in camera's, so personally I think that theory is doubtful. I'm sure others will disagree with me and I'm open to be convinced to the contrary.
One thing that's true though, is that if the scope's lenses are centred light will be arrive at your pupil in a direct straight line behind the centre of the ocular lens instead of being at a slight angle and I think that will help to minimise parallax error. (possibly)
Is it worth doing? - well it can't hurt so why not, but I wouldn't lose sleep over it personally