  Coulomb interactions strongly influence the spectrum and the wave functions
of few electrons or holes confined in a quantum dot. In particular, when the
confinement potential is not too strong, the Coulomb repulsion triggers the
formation of a correlated state, the Wigner molecule, where the particles tend
to split apart. We show that the anisotropy of the confinement potential
strongly enhances the molecularization process and affects the performances of
quantum-dot systems used as spin qubits. Relying on analytical and numerical
solutions of the two-particle problem -- both in a simplified single-band
approximation and in realistic setups -- we highlight the exponential
suppression of the singlet-triplet gap with increasing anisotropy. We compare
the molecularization effects in different semiconductor materials and discuss
how they specifically hamper Pauli spin blockade readout and reduce the
exchange interactions in two-qubit gates.
