There is a con to almost anything on a boat. Everything on a sailboat is a compromise. That said, storing the pole on the mast
is very convenient and out of the way. The cons are a little higher weight (that is not very important), a little more windage, and the cost of installing the track and fittings on the mast necessary to manage the pole if you do not already have them.
Carrying the pole on the mast can be very convenient. The Pardeys have a chapter in one of their books
- I think its The Capable Cruiser- on rigging
up a pole on the mast for easy handling.