TEI recommended practice is to specify this attribute. When the <tagUsage> elements inside <tagsDecl> are used to list each of the element types in the associated <text>, the value should be given as false. When the <tagUsage> elements inside <tagsDecl> are used to provide usage information or default renditions for only a subset of the elements types within the associated <text>, the value should be true.
If the partial attribute were not specified here, the implication would be that the document in question contains only <hi>, <title>, and <para> elements.