As someone who was a breeder/hand-raiser for over 20 years, I can tell you, with the utmost respect to you and no disrespect meant at all, that you are being extremely naive if you think that "you know all the signs/symptoms of egg binding" and you think that you will be able to tell if your bird is carrying Follicles or partially/fully formed eggs. That's just not how this whole thing works unfortunately, I wish it was but it's not...Not at all in ANY way...
If your Green Cheek does happen to be a female, she could be carrying/forming Follicles at any time and you'd have absolutely no idea at all. And the fact of the matter is that the typical amount of time you have between a bird forming an egg and dropping it into their Oviduct that is way too large for them to pass, OR having any size of egg, even a normally sized one, miss the Oviduct and drop into her Peritoneal-Cavity (100% fatal without surgery in both of these situations, Sunny's experience above that just happened last month is the perfect example) is less than 24-hours, depending on the situation it can be less than a few hours before your bird is dead.
And that's only one reason to know what your bird's gender is, there are knowing different hormonal-behaviors between males and females, what they mean, and how to quell them. Then there are the many different illnesses, diseases, and physical conditions that your bird can develop that are strictly gender-related, such as different reproductive cancers, different hernia's of the lower abdominal and pelvic areas, etc.
***I could go on and on, but the bottom-line is that I have seen/heard about/read about hundreds of situations (a lot right on this forum) where someone's bird has become ill or suddenly started suffering from type of hormonal issue, and because they didn't know what gender their birds were, they couldn't immediately rule-out certain things such as egg-binding (which can look like a hundred other medical conditions and illnesses too, keep that in mind), an Inguinal Hernia, certain reproductive cancers, common growths such as Ovarian Cysts and other female reproductive tumors/growths whose signs/symptoms are exactly the same as a hundred other issues/illnesses, etc., and BECAUSE THEY DIDN'T KNOW THEIR BIRD'S GENDER, THEY WERE FORCED TO HAVE EXTRA DIAGNOSTIC TESTING DONE TO RULE-OUT EVERYTHING THAT IT COULD POSSIBLY BE, INSTEAD OF JUST BEING ABLE TO SAY "WELL WE KNOW IT'S NOT THAT BECAUSE HE'S A MALE", OR "WE KNOW THAT IT IS PROBABLY THIS BECAUSE SHE'S A FEMALE"...
****SO if you want the best answer I can give you as to why it's very irresponsible to purposely NOT have your bird DNA-Tested so that you know their gender, it's because in the future, whether it's tomorrow, next week, next month, next year, or like in Sunny's case 7 years from now, your bird could become sick or be suffering pain from a physical/medical condition, illness, or disease, and simply because you chose to NOT have your bird DNA-Tested to determine their gender today, which you could easily do for less than $50 with no risks at all, you could not only be potentially paying hundreds if not thousands of dollars on diagnostic tests that you would NOT have to have done if you would just spend the $50 or whatever it is today, BUT ALSO YOU WILL HAVE TO PUT YOUR BIRD THROUGH THESE DIAGNOSTIC TESTS THAT CAN BE PAINFUL, STRESSFUL, AND VERY RISKY AND POTENTIALLY FATAL BECAUSE THEY REQUIRE ANESTHESIA, simply because you are choosing to not have a simple, non-invasive, cheap Blood or Feather DNA-test done now so that you'll know your bird's gender 100% and can IMMEDIATELY RULE-OUT a dozen or more possible medical issues/diseases/illnesses immediately....
I'd say that's more than a good enough reason to always get all of your birds DNA-tested ASAP...Hell, you can even order a test-kit online for $20-$30 and simply pluck a few chest-feathers, send them in the mail to the lab, and you'll have your answer a week later...And I can't imagine that having it done by your Avian Vet for one bird by a Blood DNA-test, which only requires literally a drop of blood which they can get by doing a simple toenail-clip, they don't even have to do an actual blood-draw, that it would cost more than at the very most $50-$75, depending on whether they charge you an office-visit in addition to the DNA-test cost...You can even order the Blood DNA-test online and do it at home as well by simply clipping a toenail, putting a drop of blood on the little cardboard-card they supply to you in the test-kit, and have the blood-result in a week or less for around $30 total! And all you need is a pair of nail-clippers and some corn-starch or Qwik-Stop!!! Painless, stress-free, easy, quick, and could potentially save you hundreds and hundreds of dollars in diagnostic testing in the future, if not more, and more importantly save your bird from having to have these diagnostic tests done in the first place, save them from possibly having to go under anesthesia, save them all of the stress, AND YOU WOULD ALSO BE GETTING A DIAGNOSIS AS TO WHAT WOULD BE WRONG WITH YOUR BIRD SO MUCH MORE QUICKLY BECAUSE YOU WOULD BE ABLE TO RULE-OUT SO MANY POSSIBLE CONDITIONS, ILLNESSES, AND DISEASES BECAUSE YOU'D ALREADY KNOW YOUR BIRD'S GENDER...And when a bird becomes seriously ill, every second counts, let alone minutes to hours of risky diagnostic testing...
So I think the better question here would be "Why the hell wouldn't you get your bird DNA-tested for gender ASAP?"...
) and the test just confirmed that guestimate. 
