Many look towards the Nexus devices for the clean Android experience. And given that, there is often less reason for users to be looking towards third party ROMs. But that being said, some may still prefer to have their Nexus device rooted. There are a variety of options, one of which is for backing up. Regardless of your personal reason for rooting though, there is some good news in that CF-Root has been released for the Nexus 5.
This one comes by way of Chainfire and the details have recently been shared over on the xda-developers forums. CF-Root, for those not familiar, is touted as being the root option for "rooting beginners." That is to say the process is fairly simple and will work on Windows, Mac and Linux. And as a bonus, this option not only roots your phone, but also unlocks it during the same process.
CF-Root will install the SuperSU binary and APK. The process is limited to just a few steps, which begin with downloading and extracting the "CF-Auto-Root-hammerhead-hammerhead-nexus5" zip file. From that point you will need to boot your Nexus 5 into bootloader/fastbook mode and then connect it to your computer. The bootloader mode can be reached by holding VolumeUp+VolumeDown+Power buttons.
After that, you will need to enter a few commands. These all vary slightly depending on whether you are using Windows, Mac or Linux. Either way, all necessary commands (along with the previously mentioned zip file) can be found on the xda-developers thread.
Now for the warning, while this can be done before of after the initial setup -- you should know that this method will wipe all your data. Bottom line here, if you are using this method to root your Nexus 5 -- make sure you either do it before you set up your device, or be prepared to re-build everything from memory and backups.