It's not neccesary at all unless the palm was shade grown. You can untie them.

I agree. I'll admit I don't have a lot of first-hand experience with this. But nurseries always do this...I guess to minimize the risk of water stress on the plant due transpiration through the leaves.

After I got two big ones they told me to leave them tied for 2-4 weeks. I didn't understand so I did some research. As it turns out, most all palms (except for a few like Sabal Palmetto) benefit from leaving ALL the green fronds on and not tying at all...all of this provided that you sufficiently irrigate the palm until it gets established.

Of course the nursery (the same one providing the guarantee on the plants!?) has no way of knowing if you are going to do that. I think that's why they always cut them and tie them.

Of course cutting and tying them also facilitates moving them...But if you are going to water them regularly then definitely untie them! Just my two cents...

Ref: http://ceventura.ucdavis.edu/files/47943.pdf