XF 2 custom fields users VS custom fields resources

[Robert9]

Resources have

• xf_rm_resource_field
• xf_rm_resource_field_value

and
- xf_rm_resource.custom_fields

for threads we have the same situation.

but Users have

• xf_user_field
• xf_user_field_value

All three have a view to show values for custom_fields.

But why the information is saved twice for resources and threads?

Is this done to show the infos on thread_list and resource_list without to join another table?
But normally we dont show this infos (as long we dont use one of the filter addons)