To separate items in a series. . . . The city needs healthier businesses, new schools, and improved housing. To separate coordinate adjectives. . . . A tall, sleek skyscraper is not needed. To set off absolute phrases.
Domestic recycling having succeeded, the city now wants to extend the program to businesses.
Many businesses, their profits already squeezed, resist recycling. To set off contrasting elements. The essay needs less wit, more pith. His generosity, not his good looks, won him friends. To separate dates, addresses, place names, and long numbers.