I kept on looking for guidelines, and found this in MSDN:
Choosing Between Global and Local Resource Files
You can use any combination of global
and local resource files in the Web
application. Generally, you add
resources to a global resource file
when you want to share the resources
between pages. Resources in global
resource files are also strongly typed
for when you want to access the files
programmatically.
However, global resource files can
become large, if you store all
localized resources in them. Global
resource files can also be more
difficult to manage, if more than one
developer is working on different
pages but in a single resource file.
Local resource files make it easier to
manage resources for a single ASP.NET
Web page. But you cannot share
resources between pages. Additionally,
you might create lots of local
resource files, if you have many pages
that must be localized into many
languages. If sites are large with
many folders and languages, local
resources can quickly expand the
number of assemblies in the
application domain.
When you make a change to a default resource file,
either local or global, ASP.NET
recompiles the resources and restarts
the ASP.NET application. This can
affect the overall performance of your
site. If you add satellite resource
files, it does not cause a
recompilation of resources, but the
ASP.NET application will restart.
When you make a change to a default
resource file, either local or global,
ASP.NET recompiles the resources and
restarts the ASP.NET application. This
can affect the overall performance of
your site. If you add satellite
resource files, it does not cause a
recompilation of resources, but the
ASP.NET application will restart.
So it seems that it's really up to the programming team to weigh the pros and cons of each method and choose what's good for them.