@janour
Thanks for making your font normal size at last. Now, please have a look through the answers and if any were helpful: press the Thanks button.

If you're flashing both, always do the emmc first and do Not allow device to boot until the fiasco image has been flashed.

Roughly speaking:
The eMMC is the main internal storage. You shouldn't need to wipe/reset/flash this unless you sell your device or for whatever other reason find it gets full or somehow (e.g. -devel s/w) corrupted.
i.e. it sets/resets everything in the /home and /opt folders

The FIASCO image sets/resets the rootfs (/root) and I think some of the other top level ones too (Someone please clarify). This is the one to use if you just need to clear out unwanted or faulty s/w, though you may need to go through /home or /opt to remove settings folders from software you've removed by flashing the device.