These filters will automatically tell Pods relationship fields to support multiple post types or taxonomies instead of just being tied to one. This is done by changing the default
where clause used by Pods to determine what kind of content is returned for the various areas of input (selects, checkboxes, list fields, ajax autocomplete, etc). This is by far the simplest way to customize a related field, but it also has it's drawbacks (see notes below).
You must relate the relationship field itself to a NON-POD, any post type not created or extended by Pods will do. The same goes for taxonomies. Don't worry, this doesn't mean you are unable to relate your field to any other Pod, it's just the field setting itself that needs to be set. Your filtering below will handle what it's going to truly be working with from a relationship aspect.
Failing to do this will cause any data you save to not be returned by Pods because when a relationship is related to a Pod it has extra checks to limit