Try it and see. It's not the standard advice that's given, but I think we have to be open to new possibilities. If it were possible to keep the shaft in the palm and still remain as loose as a goose then maybe there might be advantages. I'd be worried about the loss of reach, and perhaps fine control over the blade orientation, but perhaps that's just a matter of practice. It is possible that the advice you were given was part of a package of things that work together to address a particular shortcoming, perhaps.
But the message here is clear: whatever you do, try to stay as relaxed as possible. If using the palm means that you tense up then you might lose any theoretical gains.
It's an interesting and unusual suggestion. I'm going to give it a go today. It doesn't sound "right" to me - but then again as Dave Kalama pointed out, there's not much about a good paddle stroke that is intuitive.