For the most part,it is just done for cosmetic reasons.
You just need to smooth out all the sharp edges that could cause local hot spots that can cause potential preignition.
Really ,you will not see any performance gain.
If the chamber is smoothed out, it can be able to clean up carbon deposites a bit easier than a rough chamber when injecting alcohol or water injection,,,,but even w/rough chamber the use of water or alcohol injection will keep the chambers clean.
MBHD
