The Spaniards had galleons, and they needed a natural harbour. You can't just disembark on any piece of coast. If you have a beach, the ship needs to anchor far from the coast; depending on weather this may be simply impossible.
A row boat would allow to disembark a few people, but not horses, armoured knights, siege engines, food carts, etc....
You could make an argument that boats should be able to scout coastal regions, although I doubt the coding trouble is worth it, but disembarking an army is not realistic.
Well, not a whole army. A single unit... the feature I proposed would prevent moving large amounts of troops, of course.
At least you cannot say it's unrealistic for a noble to hire a ship and crew, and ask them to drop him off anywhere along the coast, possibly taking along an infantry unit.
