Different types of downloads on Cyanogen OS Website ** This question is for Cyanogen OS and not Cyanogen Mod.

On the Cyanogen OS download page, for my device (YU Yuphoria), I see 3 different downloads for my device, i.e.

cm-12.1-YOG4PAS47N-lettuce-signed-fastboot-5d674b9b61.zip

cm-12.1-YOG4PAS47N-lettuce-signed-806afa8c62.zip

cm-12.1-YOG4PAS47N-lettuce-boot-debuggable-c915697c50.img

It is clear that the first one is the firmware which is to be flashed over fastboot, but I'm skeptical about the second &amp; the third one..

What do the 2nd &amp; the 3rd link provide?
Signed fastboot zips: 
  These contain the complete rom and can overwrite everything including your data partition. These cannot be flashed via recovery - extract their contents and flash via fastboot.
  
  Signed zips:
  Normal, stock or TWRP recovery flashable zips that won't overwrite your data partition.
  
  Boot-debuggable images: (This is only for developers/testers)
  These are boot images (kernels) that enable adb root and the developer menu options. To be flashed via fastboot. (e.g.fastboot flash boot cm-12.1-YOG4PAS47N-lettuce-boot-debuggable-c915697c50.img)


Source: http://forum.xda-developers.com/oneplus-one/general/official-cm11s-roms-ota-updates-t2906746