You could spend hours making your cable routing as perfect as possible.
Routing some cables through the back of the case during the build process is a good first step toward a clean build. But this is where you'll also shove any extra cable slack through the back panel, break out the zip ties to neaten things up and, then, put the side panels back on. You could spend hours making your cable routing as perfect as possible. But just spending 15 minutes making an effort to clean up your cables after your system boots for the first time can make a huge visual difference in how your final build looks.