According To GAO:

Underutilized properties present significant potential risks to federal agencies because they are costly to maintain and could be put to more cost-beneficial uses or sold to generate revenue for the government.

Some federal agencies [such as the U.S. Postal Service] have been granted authorities to enter into enhanced use leases (EUL)—typically long-term agreements with public and private entities for the use of federal property, resulting in cash and/or in-kind consideration for the agency—or to retain the proceeds from the sale of real property.

Officials at USPS, which has authority to enter into EULs and sell real property and retain proceeds, said that the Postal Service prefers to sell or exchange unneeded
property. Officials said that USPS’s authority provides the agency with a strong incentive to actively sell or exchange underutilized property that has a high value.
Because of the relatively streamlined process to sell real property, compared to other agencies, and its ability to retain and use sales proceeds for any USPS purpose
without further congressional action, it has little incentive to enter into EULs and rarely does so. Three former USPS properties that were sold or exchanged in the
past few years were initiated by other parties wanting to purchase the building or land. For example, the state of New York approached USPS in the 1990s about
purchasing the Farley Building in Manhattan, a historic, 1.4 million-square-foot building across the street from Pennsylvania Station to redevelop the building into a new train station to be named the Moynihan Station. USPS sold the Farley Building in 2007 and is in the process of consolidating its operations into two other existing buildings and 250,000 square feet of leaseback space in the Farley building. According to USPS officials, the sale of the Farley building generated financial proceeds to USPS,26 reduced deferred maintenance costs, consolidated USPS operations into less space overall, and resulted in reduced operating costs.

GAO footnote: USPS official said that the Postal Service originally agreed to sell the Farley building for $230 million, including $55 million in a deferred purchase price that will not be paid until the commercial component of the development is built. The official said that as of January 2009, USPS has received $195 million, which is $20 million more than was expected because of inflation and other factors.

In the other two cases, in Denver and Scottsdale, Ariz., USPS exchanged old post offices with various parties (the city of Denver and a health care company) that sought the
postal property and financed new post offices. In both cases, according to USPS’s analysis, USPS benefited financially from the transaction, as well as gaining modern
and more efficient facilities in return for older ones.

source: GAO