GB difference Live vs Recovery = Why?

[n8chavez]

If the Windows partition (C: drive) is BitLocker encrypted, the image file generated in WinPE will be larger because BitLocker may not be unlocked in WinPE, in which case the program performs a "Sector by sector backup", which means that all sectors will be backed up.

Does WinPE image have any compression?   
Does WinPE image size essentially equal the size of the disk being imaged? 

I'm just now grasping what a "Sector by Sector" image is/does.  
I imagine if my disk is healthy.  I don't need to regualry create "Sector by Sector" images.  
I'm now wondering whether I should incorporate  "Sector by Sector" images in my backup routine.  

Sector by sector imaging means there is some sort of encryption on the disk that the imaging program cannot read and distinguish from any other data.  In that case, the image of the entire disk is made without compression or exclusion.  It is an exact 1:1 forensic copy.  Without encryption this is not needed, but if the disk in encrypted this is required.