The verb "compose" comes from an old french meaning "to put together". These days composing is not only about writing music notes and instrumentation. Composer is putting together samples, voices and electronic instruments and because paying a whole orchestra is really expensive, composer must be able to produce a whole song just by himself or with the help of other musicians in studio.
Games for computers and mobile devices are a typical example, when good music is needed and paying an orchestra with a conductor is out of the question. Not just because it costs too much, but often there is no need for an artistic live performance.
“I like to compose on some ready-made picture, video, intro, excerpt from the game. The music should resonate with the gameplay of course, it cannot be too complicated but just go with the flow. Player should not be disturbed. It is as well nice when music is listenable just as it is. Not within the game necessarily, but just as music for plain listening.” Ondřej
background music for sci-fi game