I work on documents in Metric, US, and also column inches using Picas and inches depending on the client. It would be highly beneficial to have the document keep the units that the layout was originally created in. An example: If someone creates a document that is A4 size and builds all of the grids and so forth with metric units, it would be much easier to have that set as the default for the document, rather than having to guess which measurements someone might have used for their grid system or layout.
Likewise all of the styling would work the same as well.
