Main risk of a nose osteotomy is the bruising associated with rhinoplasty. Osteotomy is needed to improve the appearance of your nose and make dorsal aesthetic lines (DAL) from defined. For asian rhinoplasty, it may also be needed to build the bridge of the nose by using a graft. Regarding your second question, yes, nose can be made straighter. Deviated or crooked nose can be because of cartilage or bone. For cartilage deviation, it can be improved by taking part of cartilage out and adding a graft surrounding it. For bony crooked nose, you definitely need osteotomy to improve. Risks associated with most of rhinoplasty is prolonged swelling and some bruising. If osteotomy is not done properly, it can cause crooked look but that is less than 5% chance of happening.