The ultimate spin relaxation channel for spin qubits in quantum dots involves spin-orbit coupling and phonons.I will review our theoretical realistic comprehensive modeling [1] of the phonon-induced spin relaxation in GaAs and Si coupled quantum dots,exploring a wide regime of the parameter space comprising interdot tunneling,magnetic field magnitude and orientation,and the crystallographic orientation of the coupled dots.I will discuss the special role of spin hot spots-anticrossing regions in the parameter space in which the spin relaxation rate is enhanced by orders of magnitude,and show how they imprint a unique signature of the crystal and structure anisotropy in the spin relaxation parametric landscape.Both single-electron and two electron (singlet-triplet) spin relaxation is affected by the spin hot spots.I will also briefly discuss complications in the tunneling and interdot-coupling in topological insulator [2] and graphene [3] quantum dots,due to the Dirac band structure.Supported by DFG SPP 1285 and SFB 689.