What's the purpose of an array of same VALUE capacitors?

If you count the power pins on the IC, and the supply decoupling caps of the same value, you'll probably find a 1:1 correspondence. This indicates you are expected to place one per power pin, as close as practical to the pin, to minimise the effects of trace inductance.

They are usually just multiple decoupling capacitors on the various pins of a IC that are cumbersome to show in their physical location to each pin on a schematic.

This is not typical, but... I once had to change a design to use multiple smaller value caps because the mechanical team made the fit so tight that the larger valued caps we could get were simply too tall. We could get shorter caps, but not in time for our deadline, so we punted and used smaller valued, shorter caps and got the prototype ready for its demo.

As far as I know, the smaller caps were retained into production.