Why would another country ever willingly choose to adopt the US dollar as that country’s official currency?

A few nations besides the United States use the U.S. dollar as their official currency. Ecuador, El Salvador and East Timor all adopted the currency independently; former members of the US-administered Trust Territory of the Pacific Islands (namely Palau, the Federated States of Micronesia and the Marshall Islands) decided that, despite their independence, they wanted to keep the U.S. dollar as their official currency.