In economics, politics and society examples abound in economics, politics a
nd society where agents can enter partial cooperation schemes, i.e., they c
an collude with a subset of agents. Several contributions devoted to specif
ic settings have claimed that such partial cooperation actually worsens wel
fare compared to the no-cooperation situation. Our paper assesses this view
by highlighting the forces that lead to such results. We find that the nat
ure of strategic spillovers is central to determining whether partial coope
ration is bad. Our propositions are then applied to various examples as ind
ustry wage bargaining or local public goods.