The complexity of your development proposal will dictate what type of documentation you submit in support of your planning application (i.e. in addition to the completed planning application form and drawings).
Cork City Council requires all planning applications to include a Planning Support Statement. This simply explains:
If you are proposing a complex or large-scale development and aren’t familiar with the planning system you may wish to request a pre-planning consultation and / or support from a professional planner and/or other disciplines (e.g. an architect).