what practical use would a substance with a very high specific heat have?

Answer 1

As Heat accumulator. For example, in a place with very cold winter, this substance if properly arranged, may keep warm long after the fire from the fireplace has extinguished (Maybe late at night when you are cozy and warm in your bed hugging your loved one and don't like to bother waking up to put more wood in)

Answer 2

Tungsten (metal)
is used for those coils that are in like every kind of light bulb because of its high specific because it needs to stand up to countless hours of continous heat and energy passing through it

Answer 3

As a heath storage.
For instance to accumulate heath by day and release it by night.

Answer 4

as a cooling fluid