There is some benefit to Makefile processing speed, if that's a metric that affects your build.
With one or two $(shell) calls, it won't matter at all. If you start to approach dozens or hundreds of calls, the extra overhead of all those shells can to be noticeable. Especially if your Makefile is automatically triggered on file changes or something.
The Guile approach stays in one process, but that has no value in the context of make, which launches external programs as its principal paradigm.