"the cherry on (top of|) the (cake|sundae)" 的定义和意义

What is the origin of the idiom "the cherry on the cake" and when to use it?

The origin of the phrase "the cherry on the cake" is uncertain, but it may be related to the common practice of topping desserts with a cherry, such as a cake or a sundae. The phrase was first recorded in the mid-19th century, and it has been used to denote an additional benefit or enhancement to an already good situation ever since.