Originally Posted by
Evie
Dunster, as the pattern called for, I started with 5" charms and the HSTs finished at 4-1/2". I sewed with a scant 1/4" seam as directed and the HSTs turned out fine, with just a smidge trimmed off. So now I'm inclined to go with Irishrose's explanation that pattern creators and quilting instructors use the 7/8" addition as a cushion. Now, if I'm in a pinch and need a few extra inches of fabric when making HSTs, I will keep this in mind and cut the pieces with less than the 7/8" allowance asked for -- and making sure I sew the seams extra carefully. 
I love learning something new every day! Thanks.
No, I can assure you that the 7/8" is not padded at all. When you say that they "finished" at 4.5" do you really mean that they measured 4.5" with the raw edges showing? That would mean that they actually FINISHED at 4" (or a shade larger if you didn't trim), as expected.