In cyclohexa-1,3,5-triene the molecule has 3 single bonds and 3 double bonds where all the electrons are localised. As a result the energy needed to hydrogenate cyclohexa-1,3,5-triene is (3x -120kJ/mol) = -360kJ/mol.However, benzene is a planar, aromatic molecule so all of the pz orbitals overlap. The overlap of the pz orbitals form a ring of resonance and allows all 6 pz electrons to be delocalised across the ring. The delocalisation of the pi electrons contributes to the stabalisation energy of benzene. This extra energy from resonance means benzene has a lower hydrogenation energy of -208kJ/mol and is more stable than predicted.