O2 sensor dilemma

[fufiwisi]

hey,
ive searched for a while now and cant really find too much info.
running a sr20 with a 20g turbo according to what the guy told me. definitely not the t25 turbo I can say that at least. looking over the car today and noticed that the guy had the o2 sensor out and the bunge was capped off. the car has been running fine and haven't noticed too many problems with it. wondering if I should get a o2 sensor and put it in or just run without one. is it safe to run without one.
talked to one of my boys and he says the car will just run off the pretuned map for fuel mixtures.
going to be taking my down pipe off today and slap in my wideband soon so I can read my afr and hope im not running lean. please help