To use in cases when you have multiple cachet sources.
Sometimes resources can have the same name (e.g. beaker) but they are pointing to a different server, so to avoid overriding use label.

For example:
Let's say we have 2 cachet sources.

On both of them we have a resource called beaker, if we won't use a label the beaker resource will be overridden.
Use a label to distinguish between the cachet sources (e.g. internal/external/...) so now the resource will be called [<LABEL>: <RESOURCE_NAME>] (e.g. internal: beaker).