Going for a gastroenterology endoscopic submucosal dissection soon to remove a sessile polyp. i plan to say no to blood transfusion or blood products. (was asked last general colonoscopy by anesthesiologist if wanted). any advantage in saying no?

The blood supply these days is exceedingly safe. Your procedure will most likely go well whether or not you say you do not want blood products. However, in the very unlikely prospect that you develop bleeding from the procedure, they could be life-saving. I usually recommend taking them with the agreement that they should only be given if absolutely necessary. Good luck.