In this case: doesn't matter so much. Small text interpolations should be fast. In the more general case, a variable might be bound to a shell command, a huge l

In this case: doesn't matter so much. Small text interpolations should be fast. In the more general case, a variable might be bound to a shell command, a huge list of files, or built-in Make functions doing a lot of work. And you might be using that variable in a thousand places. It makes sense not to repeat work that doesn't need repeated. Even more so if it could significantly slow down the build.