Sums are meant to be used. Obviously you shouldn't flash in base so you have this available, but trading flashes with enemy mid level 3 is usually a good idea anyway, this just makes it even better.
I used to play voli jungle duo with a friend, if you approach from behind the skinny wall dividing river from raptor camp's area, wait for them to push up a little, and q-flash the wall-instant fling, it's like 45% fb, 45% flash and fb, and 10% just flash.
Obviously this is a specific use case, but the number of gank paths mid go from like 8 to 14-16, if you can jump walls without burning your gap closer/cc, and being able to do it every 10s is absolutely insane.