Welcome ilse-sophie!
Like almost everything else in quilting this question has two schools of thought!
Yes, it will distribute the bulk, and if you want to stitch in the ditch you can truly be "in the ditch". But....by stitching there, you will only be stitching on the threads that hold the seam together. The quilting lines really can be almost invisible, and some people are OK with this if the piecing is done on the machine. However, it the piecing is done by hand, the seam is probably not strong enough for this method.
If you press the seams to one side or the other, you can only just try to stitch on the low side of the seam and some people say that this results in a stronger quilted line. The difficulty comes when seams aren't always pressed to the same side, and you have to check (by feeling) which is actually the low side of the ditch.
Or...you can just choose one side (say the lightest value fabric) and always stitch on that side, no matter where the seam allowance falls. I call this "Near the ditch" and often do this on utility quilts.
It will probably depend on the destiny of the quilt, but how you do it is up to you. There are no quilt police on TQS!!