You can create a new assembly file, or you can add the same components to the existing assembly file. Each copied component creates a new file. If you prefer, you can reuse components instead of copying them.
For each configuration you can decide which version of assembly is used, and whether a particular assembly must be unique. If component must be unique, copy it instead reusing. If you made changes in copied part it's it not.
For example: front side plate of drawer case has different dimensions, depending on drawer model in this case you need to create independent side plate copy. Drawers handle in different drawers may be the same, so you can reuse existing copy. If you have standard component, used in many assemblies it is convenient to place this component in library and reuse it' as needed. A single library can be used across any number of products.
Checked checkbox in front of a component means that specified component participate in component copying/renaming operation. Unchecked components will be reused from original assembly.
