  We study molecular outflows in a sample of 45 local galaxies, both star
forming and AGN, primarily by using CO data from the ALMA archive and from the
literature. For a subsample we also compare the molecular outflow with the
ionized and neutral atomic phases. We infer an empirical analytical function
relating the outflow rate simultaneously to the SFR, $L_{\rm AGN}$, and galaxy
stellar mass; this relation is much tighter than the relations with the
individual quantities. The outflow kinetic power shows a larger scatter than in
previous, more biased studies, spanning from 0.1 to 5 per cent of $L_{\rm
AGN}$, while the momentum rate ranges from 1 to 30 times $L_{\rm AGN}/c$,
indicating that these outflows can be both energy-driven, but with a broad
range of coupling efficiencies with the ISM, and radiation pressure-driven. For
about 10 per cent of the objects the outflow energetics significantly exceed
the maximum theoretical values; we interpret these as 'fossil outflows'
resulting from activity of a past strong AGN, which has now faded. We estimate
that, in the stellar mass range probed here ($>$ 10$^{10}~\rm M_{\odot}$), less
than 5 per cent of the outflowing gas escapes the galaxy. The molecular gas
depletion time associated with the outflow can be as short as a few million
years in powerful AGN, however, the total gas (H$_2$+HI) depletion times are
much longer. Altogether, our findings suggest that even AGN-driven outflows
might be relatively ineffective in clearing galaxies of their entire gas
content, although they are likely capable of clearing and quenching the central
region.
