Professional? If you hold a CPL or an ATPL, your licence will only be valid if you hold a Class 1 EASA medical certificate. You also need a Class 1 EASA medical certificate in order to train for a CPL or an ATPL.
Individual? Anyone wishing to train for a private pilot’s licence will need to obtain an initial Class 2 or LAPL medical certificate or an national private pilot licence NPPL medical declaration as part of the licensing requirements.