Like Indonesia's Kampungs, Polders synergize well with the Dutch naval bonuses and make settling on or near the coast much more viable. Polders can also provide a useful boost to lake tiles, especially combined with Huey Teocalli.
Polders which are built adjacent to other Polders receive additional bonuses to Food. This is increased once you have researched Replaceable Parts. While most maps will have a larger number of Polder viable coast tiles, it is easier to harness this adjacency bonus with lake tiles due to the enclosed nature of a lake, which makes it easier to satisfy the "3 or more adjacent land tiles" restriction. Usually most (if not all) lake tiles will satisfy the condition, allowing you to simultaneously benefit from the Adjacency bonus! In fact, a Dutch player may be the best suited of all to take advantage of lakes in the game!
The Polder's penalty to movement applies to all naval units, including embarked units.
Despite polders being reclaimed lands enclosed by dikes near a shore area in real life, it is still a water tile in the game accessed by naval units, and land units that are embarked.
Most see the shoreline as an end. For the Dutch, the coastline was a challenge and an opportunity. The Netherlands spent 800 years reclaiming a country from the sea, using dikes, canals, levees, and pumps. Polders are the low-lying bits of land revealed when the water recedes.
The Dutch constantly maintained their polders to prevent the sea from reclaiming the land. Over the centuries, they mastered the art of keeping water out and reversing the effects of erosion. Today, more than a quarter of the Netherlands remains below sea level, leaving the country in a continuous game of tug-of-war with the North Sea.