Prism99

It depends a lot on the quality of your piecing stitches. I used to fix up vintage sewing machines for charity and often needed to adjust machines to get a good, secure stitch.

Secure stitching requires that the top and bobbin tensions be set correctly. The tensions need to be balanced so that the threads meet in the middle. When they don't meet in the middle, one thread lies flat against the fabric and can be easily pulled out. In addition to being balanced, the tensions need to be somewhat tight. If you have a balanced stitch where the top and bobbin tensions are loose, you can pull apart the seam and easily see lots of the stitching thread in the seam. When the tensions are tight the way they should be, very little of the thread is visible when you pull the seam apart.

Stress on the seams comes from everyday handling, sitting on a quilt, washing and drying a quilt, hanging, etc. Quilting reduces the stress on seams. The closer together the quilting lines, and the more often quilting crosses over seam lines, the less stress there is on the seams.

In your particular situation, the seam within the channel will be stressed more than others in the quilt because you have a long seam line that has no quilting stitches running over it. If the stitches used in piecing the seam are tight and secure, then there will be enough support so that no single thread is ever taking all of the stress. If, however, the piecing stitches are loose because of one of the reasons above, sooner or later the stress will be concentrated on a single thread and that thread will break.

Edit: Shortening stitch length does make for a more secure seam; however, it also adds thread to the seam and makes un-sewing more difficult. That would be my last resort if I couldn't get the tensions right on my machine.