From the linked piece about Alpha Cen A & B...

As lithium burns at temperatures close to 3 MK, the observed
surface abundance [Li]s (H = 12) is often used as a
probe for theories of transport processes at work beneath the
external convective zone. The microscopic diffusion alone is
not efficient enough to explain the lithium depletion observed
in the Sun and stars; thus, there is a need for an unknown physical
process, e.g. a turbulent mixing, acting in the radiative zone
just beneath the outer convection zone – e.g. Schatzman (1996),
Mont`alban & Schatzman (2000) for a review.

...thus why Lithium is a significant sign of 'something' going on in stars. If planet formation stirs a star up, then the problem abundance is neatly explained. Further on in the article...

Table 3 reveals a good agreement between the measurements
of the lithium abundance. CenA presents a depletion close to
the solar one ([Li]s = 1.11, Grevesse&Sauval 1998) while, in
Cen B, the lithium is clearly more depleted. The assumption
of a common origin of the two stars eliminates the possibility of
a different initial lithium abundance in the pre-stellar nebulae.

...implying that both A & B should have formed planets and/or caused mutual stirring in each other.