Small multiples repeats the same chart in separate panels, one for each member of a chosen field. A monthly sales line can become one panel per region, with the same axes across panels. Readers can then compare shapes without untangling several overlapping lines.
Keep the scale consistent when the goal is to compare magnitude. Independent axes can make a small region look as large as a major one. Choose a panel field with a manageable number of members and a stable sort order. A blank segment can deserve its own panel because missing classification is part of the data. Adding a field to Legend creates colored series inside one chart; it doesn't create the separate panels that Small multiples provides.