two pleasures from one thing; double enjoyment
A set phrase originating from a TV commercial for a candy with two flavors. Used figuratively to describe any situation where one action or item yields two benefits or pleasures.
This smartphone also has a great camera, so it was a purchase that gave me two pleasures in one.
If you go shopping while taking a walk, you get two benefits for the price of one.
一石二鳥 is a more formal, proverbial expression meaning 'killing two birds with one stone,' while 一粒で二度おいしい is a casual, playful phrase from advertising.
Variant spelling using the kanji 美味しい instead of おいしい; same meaning and usage.
Originated from a Japanese TV commercial for a candy that had two flavors in one piece, hence 'delicious twice with one grain.' The phrase became a popular idiom for double benefits.