3 reasons I added scanlines to my videogame:

1. Gives the game a "grittier" feel.
2. The scanline, a color-alternating red and light blue horizontal line, doesn't look overly flashy -- but it helps unite my games color palette, which some would argue contains too many colors.
3. MOST added movement in ANY game will catch your player's attention!

Watch me add SCREEN SHAKE next! :)