Civic EG

What does the pre cat o2 sensor actually do on a d16? Currently my car is running without one and on a automatic ECU which I am replacing with a chipped ECU should I buy and install a o2 sensor or can I have them turn it off in the ECU before I get it? I have no problem doing whats best for my car but if its not really needed then I wont.

I did a search for "o2 and sensor and delete" and found a thread that explains it: http://Civic-EG.com/viewtopic.php?t=25228

Sorry was lazy lol TYVM for the link and the response in the link! I will pick up a new o2 sensor and install it asap.