Long compile times and having lots of small crates in your dependency tree, surprisingly, are related in that, as the author mentions in the article, splitting

Long compile times and having lots of small crates in your dependency tree, surprisingly, are related in that, as the author mentions in the article, splitting libraries into separate crates makes the compilation of each individual crate much faster because crates you depend on are compiled in parallel, and don't ever need to be re-compiled after the first compilation (so hot builds become much faster) while the current crate being compiled becomes naturally much smaller, hence faster to compile, when you pull chunks of it into other crates.