Examples

Example 1

Portland is home to dozens of gourmet corn dog carts; there are several in the Pearl District alone.

Using the indefinite pronoun several here indicates that it isn't important for the reader to know precisely how many fancy corn dogs stands there are.

Example 2

Nobody should ever sing "Bohemian Rhapsody" at karaoke.

It's appropriate to use nobody here because it doesn't matter who the singer is; they'll never be as cool as Freddie Mercury.

Example 3

Julie watched all of 30 Rock on Netflix in a single week.

Using all is correct because the exact amount of time that Julie spent pounding Sabor de Soledad cheese curls and binge-watching 30 Rock is unknown.