Many blogs are like parrots. Copied content and lots of advertisement. Fair enough, that’s the Internet in 2015. However, this gets annoying when some alledged smart solution is presented and copied all over the place, effectively hiding the way the product owner meant it.
For example, doing a clean upgrade of OS X. Googling around might lead you to believe that you need an USB stick for this, make it bootable, copy the right files into it etc. etc. Do you seriously think that this is what Apple had in mind?
A clean OS X upgrade via Recovery Partition or Internet Recovery is not possible. These processes allow you to either reinstall the current OS X release (using recovery partition) or install the OS X release that came with the hardware (using internet recovery).
A proper clean upgrade requires a two step approach:
1. Upgrade OS X via the App Store. This make it possible to check if everything works with the new release without wiping your disk. This is a safe process, fully supported by Apple and with the option to revert the upgrade via Time Machine. This upgrade also upgrades your recovery partition, effectively enabling step two.
2. Boot into your recovery partition and follow Apple’s instructions on how to reinstall on a clean disk. This involves starting Disk Utility and erasing your OS X partition (do not erase the whole disk!). Then start the reinstall from the recovery menu. Since you can only reinstall the currently installed OS X release, step one is required first.
So no USB sticks involved…