Possessions are samples
Each possession is a trial in which the better team is somewhat more likely to succeed. With more trials, the advantage accumulates; with fewer, luck retains a larger share. A slow game is therefore a statistical favour to the underdog, whatever it looks like emotionally.
Choosing the right pace
It follows that a strong team should generally want more possessions and a weaker team fewer. In practice, coaches often do the opposite, because slow play feels controlled and fast play feels risky. The feeling is understandable and the mathematics is not negotiable.
Where the exception lies
The exception is roster depth. A team with eight capable players can sustain a high pace that a team with five cannot, so pace has to fit personnel as well as probability. That is the legitimate version of the argument for playing slowly, and it is a different argument from preferring control.