The Flash S01e01 Workprint - !full!

The most obvious difference. Many of the speedster effects (lightning trails, the red blur, phasing through walls) are either incomplete, in wireframe/gray-box form, or replaced with temporary markers. For example, Barry’s first run after being struck by lightning might show a simple motion blur instead of the iconic orange-red lightning.

Here’s what makes it significant:

That is an interesting find. The workprint for The Flash season 1, episode 1 ("City of Heroes") is a known artifact among fans of the Arrowverse. the flash s01e01 workprint