DFU vs Recovery Mode
DFU vs Recovery:
The Difference Between Recovery Mode and DFU Mode
The main difference between the Recovery mode and DFU mode rests in iBoot. Recovery mode uses iBoot during restoring or upgrading your iPhone while DFU mode bypasses the iBoot so you can downgrade the current firmware because there is no iBoot agent during the DFU mode. Recovery mode is shown on the right with the USB cable showing on the iPhone and DFU mode is always a black screen.
What is iBoot:
iBoot is the bootloader on iOS 10/9/8/7 devices. iBoot acts on restore while iPhone is in Recovery Mode. It makes sure that you are flashing a firmware version greater than or equal to a current one. If you are not, iBoot will not allow the restore to proceed.
Firmware downgrading must be done in DFU mode. This means if you need to restore your iPhone to current version simply put the iPhone in recovery mode and iTunes takes care of the rest but if you need to downgrade your current firmware to lower one you need to put your iPhone in DFU mode.