Depends on what size. I made a quilt that used 1.5" squares, and that meant for each 1" sq of visible fabric, there was 1.25" sq of fabric in the seam allowance - and that did make for a heavier quilt, but I would not say it was "heavy". I like to sew with small pieces so it's normal for me to make a quilt that has 30-50% more fabric in the seam allowances anyway.
If you want to get an idea, take 4 yards of fabric and compare it to 9 yards of fabric, and see if that difference is too much for you.