I do not pin at all when I am stitching blocks and matching up seams. I just press my seams to oppose each other, snuggle them up and sew. I have no problems with mismatched seams.
I do pin when I am stitching on a border. I fold my border in fourths and press it to "mark" it. I do the same with the quilt top. Then I pin at the matching quarter marks and in between to keep my fabric from slipping.