“When you look at foundations, it’s much like having a family business,” Mr. Grasso said. “Some businesses get handed down to the offspring, but with other businesses, the offspring don’t want to be part of the family business anymore.”

The Rockefeller report found three drivers for a spend-down foundation: to see the impact of the gift in the donor’s lifetime, to narrow the philanthropic focus and to send more money to urgent causes sooner rather than later. Those who opted to maintain a foundation in perpetuity were motivated to address continuing problems, strengthen their family’s values and purpose, and have an impact on beneficiaries over several generations.

One of the best-known spend-down foundations is the Atlantic Philanthropies, created by Chuck Feeney, who helped found Duty Free Shoppers. Through it, Mr. Feeney has given away an estimated $8 billion.

In 2002, he decided he wanted to give away all of his money in his lifetime, setting 2016 as the date for the last of it to be donated.

“This whole notion of limited life does concentrate the mind,” said Christopher G. Oechsli, president and chief executive of the Atlantic Philanthropies, told me in 2014. “It introduces a dimension of urgency.”

That sense of immediacy was common, the Rockefeller/Campden Wealth report found, particularly for foundations that changed to a spend-down model later.

The S.D. Bechtel Jr. Foundation, which was started in the 1950s by a grandson of the founder of the engineering firm Bechtel, had for decades been making grants focused on issues the family cared about. But in 2009, Mr. Bechtel decided he wanted the foundation to focus on what he felt were imminent concerns in California — integrated water management and STEM education for children.