I just did a class from Craftsy. The teacher there recommended that you sew a few stitches in the seamline and then backstitch to secure. Then on any piece on the outside that is the last overlap to sew all the way through the seam allowance past the edge (Making sure to backstitch in the seam allowance to secure).

I found that if I sewed past the edge on all the pieces around the block then on some of the ones that overlapped it was hard to trim to a 1/4 inch seam allowance. I know this is difficult to describe in text, but it really matters when a couple of oblique angles come together.

When I paper piece, I start 1/2 inch before I place of start and 1/2 inch after the stop point, that is the way I was taught.