It does a lot! It's probably easiest for me to copy/paste the section from my textbook (sorry for the quality):
As you see there are like four different ways it can affect sounds (Khmer spelling reform, anyone?). Btw, the author uses a transliteration system where /ɔɔ/ refers to ក type letters, and /oo/ to គ type letters.
Btw, this passage is from Cambodian for Beginners by Gilbert, I can highly recommend it for a thorough yet concise source for fundamental Khmer.