Also its a good idea to approach but only when IOI is received. No IOI, no approach. The confirmation of IOI would alleviate the uncertainties and lessen the risk around failure in the event of an attempted approach
If a female were to reject your advances, the amount of possible reasons for her decision to reject you are numerous, including reasons that may not have to do with your looks / attractiveness (e.g. doesn't socialize with men from your race, strong body odor, has the impression you are poor or a career criminal based on your current clothing outfit, signs of autism, currently in faithful relationship, religious reasons, currently focused on academic studies or business ventures, risk of damage to their work / life balance etc etc...)
If you succeed in cold / warm approach and receive sex, ultimately it wouldnt matter how you did it, because the outcome would justify the means. It would be pointless to approach if the chances of success were 0%. But if you fail an attempt at approach, it may not be clear as to exactly why you failed, and you may have to retry many times before you can identify a pattern in the instances where you failed compared to instances where others didn't fail. In life, its better to be successful and not know why you were able to succeed, than it is to be a failure and not understand why you failed.
Personally, Im not interested in knowing why a female may not have any sexual interest for me, which is why I'd rather wait for IOI than go in blindly.