The seam allowance is the amount of fabric between the stitched line and the cut edge.
Standards are 5/8 , 1/2, and 1/4 inch. The 5/8 inch allowance is most often used in making garments. For quilts most quilters use 1/2 or 1/4 inch allowance.
Quilts that have large pieces are most likely to have the ½ inch seam allowance.
Quilters that are just beginning often chose to use the ½ inch allowance because it gives them a little more sewing area.
Quilt blocks that have smaller pieces are best if the 1/4 seam allowance is used. Using the 1/4 inch allowance on blocks with smaller pieces lessens the amount of fabric bulk on the pieces.
Whether you decide on a small or a large seam allowance the most important thing is to make sure that you use the exact same seam allowance on all seams and all the way across the seams. This is the only way your quilt top will fit together as you intend for it to. Make sure that you make a small backstitch at both ends of each piece.