It would certainly be a simpler solution - that or run Kodi as a native Windows application (Win32 or UWP flavour)
On the other hand Kamal may have a very particular reason for wanting LibreELEC dual boot and/or may not want to dig out and plug in a USB device every time he wants to use Kodi, or tie up a laptop USB port by leaving it permanently plugged in. Or some entirely different reason... Speed isn't always the primary motivation. Who knows?
I'm not sure what kodi on windows has to do with it.
LE booting from usb / HDD are indistinguishable when running
Advantages of running from usb:
- no need to touch windows loader
- can be easily set up on top of a running windows install
- much quicker to set up
- can be easily removed (unplug usb / remove ext4 partition and it's completely gone)
Disadvantages:
- it needs a 512MB-plus usb stick / sd card
- one less usb port / sd reader while using LE (it can be left in or taken out when using windows).
I checked on my laptop (I actually have LE on the HDD for once since installing mint) and boot times are actually about the same.
For someone who's not that comfortable in a linux environment and doesn't really like messing with windows bootloader (ie me!) there's a lot less to go wrong using usb. For linux afficionados it's probablky an inelegant solution.