Often times it is not NEEDED per se, but evidently, in terms of less electrical "noise" and voltage drop from your equipment, there seems to be something to be gained from an "optimized" electrical system with regards to overall vehicle performance. Whether that transfers into more horsepower or simply less electrical noise within your audio system is difficult to say until you actually do the project.
Grounding the computer will be relatively easy. You should have at least one ground on the housing, then there should be two ECU grounds (pin 40 and 60 on a A9L) and there should be a TFI gound (pin 14?) that can also be used. Just find those grounds on your computer (using a wiring diagram) and "T" in 14-16ga ground lines to say, a 4-6ga main and run that 4-6ga line to your negative battery post.
If you take a closer look at some of those ground kit diagrams, you will see the locations and the sequence in which they recommend.