This addon simply displays your soul shards in a more precise way.
How can it be more precise than the standard UI, if that shows exactly how many soul shards you have? The problem lies with the draenor perk "Empowered Corruption". It reads, that you have a 2.5% increased chance of proccing Nightfall. What it actually does is not increasing the chance of procs, but instead increasing the amount of shards you get per proc by 0.25. So each time you get a nightfall proc you actually get 1.25 soul shards, but the display only shows you the full shards.
This addon shows exactly how many soul shards you have, and has a warning function, that changes the color of the background of the soul shards, if the next nightfall proc would result in a waste of soulshards.
You can adjust the border thickness, the spacing between the shards and all of the colors. It will automatically show and hide depending on the spec you are currently playing, unless you toggled it off completely.
For a list of commands type /bss help