For Rogues it takes away the noise from rogue talent Focused Attacks and replaces it with a 1 second long soundless wav file. Credit goes to pharaunmizz for linking me to the guide on how to do this(dunno spelling). This is not a WoW addon it is a sound file. Scroll down to read what it does.
For non rogues it will not do anything.
To install,put the data folder into your wow folder.
If you want to Uninstall:
Delete the one file named focused_attacks_impact
World of Warcraft\Data\Sound\Spells\focused_attacks_impact.wav
what does it do?
It puts a blank 1 second long sound file in the first place that wow looks for the focused attacks sound file.