Why is the feed dog timing like this?

[Wizcrafts]

Maybe I will have to create a new forum section to discuss domestic sewing machines. Let me study on that. That way folks wanting to delve into the mechanics and design parameters of household machines may get more useful interactions than in this leather sewing machine section. This forum is really targeted at industrial leather sewing machines, not household machines that might could sew leather, nor industrial machines meant for high speed sewing of broad cloth and man made materials.

If I get the go-ahead and do create a non-leather sewing machine forum I will link to it as a sticky post.

[Gymnast]

Some sewers do light leatherwork on domestic machines or industrial machines for garment with dropfeed.

I found this information about feed timing from JUKI on more of their industrial machines for garment:

So they recommend an advance in feed timing in order to reduce variations in stitch length. A reason might be that the thread tension is applied and stitch is formed after the stroke of the feed dog finished. Therefore thread tension do not work against the feed.

What is new to me is, that JUKI propose a delay in feed timing to increase stitch tightness. In this link it is reported, that you can reduce seam pucker by retarding feed timing:

Link to book, Joining textiles

I think it can be so, that with delayed feed timing, the feed is part of forming the stitch and makes some of the local thread tension to do so. Therefore less thread tension is needed from the tensioners. The result is that you can reduce seam pucker. But with heavier fabrics or more firm fabrics seam pucker will never be a problem and therefore it can be better to advance timing to improve feed dog traction with such fabrics.