Article 4.1 CPR
"Declaration of performance
When a construction product is covered by a harmonised standard or conforms to a European Technical Assessment which has been issued for it, the manufacturer shall draw up a declaration of performance when such a product is placed on the market."
And Article 8.2 general principles of CE marking "The CE marking shall be affixed to those construction products for which the manufacturer has drawn up a declaration of performance in accordance with Articles 4 and 6.."
These articles from the CPR show that were a wood based panel is used in construction it is mandatory to be CE marked because it falls within the scope of a harmonised standard (EN 13986), which requires it to have a declaration of performance (DoP) which in turn requires it to be CE marked. This will include products such as MDF, OSB, Particleboards, flax board, plywood, blockboard, LVL and cement bonded particleboard.
For wood based panels, construction products would be uses such as wall sheathing (structural and non-structural / decorative), flooring (structural decking and floating floors), roofing (structural), sarking, boxing in etc i.e. anything used in a building or other construction works whether structurally or non-structurally.
wood based panels suitable for non-construction uses do not need to be CE marked, these uses would include furniture (including fitted wardrobes and kitchens), site hoarding, boards supplied to be incorporated into another construction product where the final product has its own performance within the construction as a consequence of all its components (e.g. doors skins within a door, it is the door that has the final performance) etc.