Suggest that you check the width of the seam before you quilt it. If it is less than 1/4" than sew the seam to the 1/4" width. You don't have to take the too narrow seam out first. If the fabric is shredding - happened to me once, even with the 1/4" seam, LQS fabric, too - do a narrow zig zag down the seam to prevent more shredding.
I make these suggestions because I am not sure that quilting down the seam will make up for a too narrow seam or seams shredding apart. And it is 1000% easier to fix seams before you quilt than after.
Just saw your response to Prism99. I have never made a quilt using knit shirts, so my suggestions may be invalid - except that it is easier to fix seems before you quilt.
Last edited by cathyvv; 02-28-2018 at 09:29 PM.