O2 sensor, need it or not?

Info I had found when screwing with a 2007 GC O2 sensors

The O2 sensor is there primarily because of emissions! A second reason is to fine tune fuel management. And thirdly they indicate the state of the catalyst.

It was developed to ensure that the correct amount of oxygen is available for a reaction to take place in the CAT which needs O2 to convert other nasty gases to form less nasty gases. (Example carbon monoxide + oxygen = CO2.

The sensors upstream (before the Cat) are important for delivering the correct amount of oxygen and for fine tuning the air-to fuel ratio. They help determine the duration of time that the injectors stay open. The oxygen sensor measures the oxygen content from the exhaust stream and from this it can figure out if the fuel mixture is rich or lean

The downstream O2 sensors are for measuring the catalyst shelf-life. This will tell if the Cat is spent and needs replacement. This sensor has no effect on the engine performance if it the vehicle is OBDI (up to 1995).