For Free

adj. Said of a capability of a programming language or hardware equipment that is available by its design without needing cleverness to implement:

"In APL, we get the matrix operations for free."

"And owing to the way revisions are stored in this system, you get revision trees for free."

Usually it refers to a serendipitous feature of doing things a certain way (compare big win), but it may refer to an intentional but secondary feature.