A common source of confusion is is the Type attribute of the file element used when creating a module to provision files in SharePoint database.
You can set this attribute to Ghostable or GhostableInLibrary or you can leave it alone and not to set it meaning that it’s “Unghostable“.
Ghostable and GhostableInLibrary –> Specifies that the file be cached in memory on the WFE. Both values specify that the file be cached, but GhostableInLibrary specifies that the file be cached as part of a list whose base type is Document Library and that you can work with the file as you would with any other file in the library ( check-in, check-out, version history).
When changes are made, for example, to the home page through the UI, only the differences from the original page definition are stored in the database, while default.aspx is cached in memory along with the schema files. The HTML page that is displayed in the browser is constructed through the combined definition resulting from the original definition cached in memory and from changes stored in the database.
If you don’t set a value this means that the file is Unghostable implying that the file will not be cached in memory in WFE and that it’ll be completely stored in the database.