Your views should concentrate on 'planning' issues such as; the planning history of the site, the visual impact of the development, affect on public amenity, access, traffic and highway considerations or the impact on listed buildings, conservation areas, or protected trees.  Matters that cannot be taken into account include; effect on property values, the character or identity of the applicant, boundary or property disputes, how the application affects a view (as opposed to the wider affect on public amenity) or issues of commercial competition.