Disadvantages of a winch vs. a tow: The height that you can obtain with a winch launch is essentially a certain percentage of the field length. Around the 50% mark I'd say -
Not if the wind is strong enough - if it is fairly strong you can 'kite' up during which the winch either stops pulling in the cable or even lets it out. Not all winches are happy doing this though and if they have a 'fluid flywheel' coupling it can overheat and the thermal plug fail - spraying hydraulic oil everywhere. I've had nearly 2,700' on a 3,500' winch run - a bit more than 50%!