He's talking about having Rufus not reformat the drive (or, if the drive has multiple partitions, preserving some of them), which, just like multiboot, is a feature Rufus will never provide. The goal of Rufus is to ensure that your USB is gonna boot, period, and I'm not going to take any shortcuts that might jeopardize that goal. Unfortunately, what most people don't seem to realize, who aren't familiar with the myriad of boot methods and the many ways in which they can fail, is that, the best way to ensure that a device will boot is to always start from a clean slate. In essence, that means completely repartitioning and reformatting the drive, always. That's not to say that, in some circumstances, and if you're lucky with the images you pick, trying to preserve existing data might theoretically work. But in a lot of case, it's going to be a major hindrance to ensuring proper boot, and I can guarantee that, regardless of how smart the application that creates your boot device is, the only thing you will gain with data preservation is that YOU are going to run in some weird errors, that will take a lot of time and effort to troubleshoot, which you wouldn't have gotten with a utility that always starts by repartitioning and reformatting the drive in accordance with the specifics of the image you are trying to boot. Therefore, if you don't want your drive to be repartitioned and reformatted, then I will kindly ask that you use another application.
Oops! Looks like I was a bit overzealous in pushing a last minute file name sanitization (and not testing it properly)... Thank you very much for being the first one to report this!! Since not too many people should have downloaded the current BETA, I have just pushed a "stealth" update for it, that fixes the issue, so please re-download and let me know if you still see a problem. The new BETA should report 2.13.1078 for its version, and not 2.13.1077. Many thanks for the report - much appreciated!!