by Chris Tyler:
Optimizing a scene, Part 1. Shapes, Instances and the Replace Selected Function
This tutorial shows the basics of using shapes and instances as it relates to replacing existing items with instances of a shape. This is very useful for optimizing a scene that has many repeating elements Part 1 is here (Replace/Exchange Selected). Part 2 is here (Replace/Exchange Selected on a more complex scene). Part 3 is here (Snap To Tool). Part 4 is here (creating piping segments).