If you find yourself in a situation where you need to make multiple duplicates of an object with equal spacing between them (fence posts, for example), you can use Maya's Duplicate Special command (Shift + D).
Select an object and press Shift + D to duplicate it. Translate the new object a few units to the left or right, and then repeat the Shift + D command.
Maya will place a third object in the scene, but this time it will automatically move the new object using the same spacing you specified with the first copy. You can repeatedly press Shift + D to create as many duplicates as necessary.
There are advanced duplication options at Edit → Duplicate Special → Options Box. If you need to create a specific number of items, with precise translation, rotation, or scaling, this is the best option.
Duplicate special can also be used to create instanced copies of an object, which is something we've briefly discussed in this article, and will further explore in later tutorials.