Why are unit nouns especially useful when they are used to modify a mass noun?

Give at least two grammatical functions of the -ing participle.

Explain the conditions in which we need or do not need to use and between premodifying adjectives.

Why are unit nouns especially useful when they are used to modify a mass noun?

determiners

the major function of prepositions

Using a genitive or a double genitive wherever possible:

I believe the reputation of our university is as good as that of any other university.

Using a genitive or a double genitive wherever possible:

Professor Smith is one of my teacher’s old friends.

Using a genitive or a double genitive wherever possible:

I found some of your old hats.

Turning the singular nouns or noun phrases into plural forms wherever possible with other necessary changes:

Tell the kid to bring a raincoat with him tomorrow.

Turning the singular nouns or noun phrases into plural forms wherever possible with other necessary changes:

She is a woman pilot.