If land has been used for a certain purpose for more than ten years (without planning permission ever having been sought) - is there any point applying for a Certificate of Lawful Use since enforcement action against that breach cannot be taken after ten years?
Quite so. It 'regularises' the legal position with regard to planning consent and any buyer's solicitor may insist on it before he is willing to allow his client to proceed.
Consider it as a planning application for which you pay the same fee as normal, you submit the same plans but for which you know the planning authority cannot turn it down. Well worth the �250 or so that it will cost you.