Question:
Why should the Allies ever bother to plan a conventional amphibious landing? Here is what you do: Plan an air drop for one para unit in a coastal hex. If the coastal hex is unoccupied, or only lightly defended at the beginning of your next turn, proceed with the operation. In this way the Allied player can plan a large number of invasions per turn using only one air droppable unit per invasion site and then choose which one to execute after seeing the exact positioning of Axis units.

Answer:
This is how it works. If the Axis leaves important areas underdefended, it pays the price. By the way, it pays to have fort counters in all minor ports, even ungarrisoned ones, just to get the extra -1 DRM on the Parachute Disruption table. It may be useful to point out here that even if the parachute battalion does grab the hex, it only owns the beach there in the following exploitation phase, not immediately. It only owns the port there for purposes of naval transport if the hex is still Allied-owned in the next Allied initial phase.

Source:
TEM 74