NefMoto

I am gutting my downpipes on my b5 s4 and I was just curious... The tune I am running right now says it has the o2s codded out but does that count for all four of them or only two? How can I check? I know the car has four o2 sensors, two post cat and two pre cat, and most of the time from what I have read when gutting the downpipes you keep the rear o2 sensor... Anyway I guess my questions are: what are the advantages and disadvantages of using/not using the o2 sensors? How can I tell if all four are coded out or if only two are coded out? Also, I supposed if you want to take it one step further, you could also help by letting me know the advantages or disadvantages of the egt delete and and even help with what I should do with my secondary cats... because I want to get rid of those too but I am not sure if I should gut them or just cut them out and replace with a straight piece of pipe...
As usual thanks in advance for all your help.

When people say the O2 sensors are coded out, they are referring to the post cat sensors after the catalytic converters.