Do the o2 sensors in the exhaust system affect performance?

[getfreshcrue]

I'm asking because I decided to leave them out because I don't have to worry about an inspection but I'll put them on if they affect performance because of the fuel oxygen ratio... or if it'll save me more gas

[mralandy]

First o2 sensor manages a/f ratio. From what I heard the 2nd one is only there to measure cat efficiency.