Why do you sometimes refer to it
as a SCANT 1/4" seam??
Each time you press a seam to the side, you can lose the
tiniest bit of block width in the crease. Across the whole
width of a block, that can mean significant loss of block
size! So, sewing with a
SCANT 1/4" seam, which is a couple threads LESS THAN a true
1/4", you compensate for that bit of lost block width!
Generally, quilters call this "using a 1/4" seam", but
the reality is that each quilter needs to find the sweet
spot on Their Own Machine, so that after pressing, your
blocks consistently come out the right size!