I certainly agreed with ckcowl. If most of the fabrics are darker than the threads then the threads probably do not need to be trimmed. However; it is a very good habit to get into - trimming them as we go. The only concern I can think of would be if there are light fabrics used in the top where the thread ends might show through and spoil the overall look of the quilt. I have quilted tops for customers, where the dark threads did show through under light fabrics on the top (sometimes it was the raveling of the top fabric, other times it was the piecing threads) - when that happens I am able to flip a top roller up on the quilting frame and trim the offending threads - or, if I don't notice it until the top is quilted I have been able to use a tiny steel crochet (sp) hook to pull the threads out.