as a longarmer, the only problem I could see is if the fray threads are dark and are seen under a light(white) solid. Otherwise, if your seems are all closed and 1/4" allowance, it shouldn't be a problem. Your LA will quickly attach the top to the back/bat and it won't be shifting much while quilting. I won't go in and trim up threads on the back unless charging extra, so if you have a dark fray thread under white sashing for instance, it would probably be left as is and may show. Definitely don't use fray check or anything else that may gum up the needle, please!