For me it is the single biggest feature addition. Just changing one file would require rebuilding the entire site in Jekyll. Something similar to a Makefile should be in place, which can track dependencies and rebuild only the affected files.
I fail to see how changing a typo in an article's content would require the whole thing to be rebuilt. Even adding a page would not require rebuilding every single page unless the new page appeared in a global navigation. Building the dependency graph automatically could even turn out to be not that hard.