The first one that is well shown with the attached exmples are when a flange requires a side angle, and the chamfer in the flat is actually removing material from the previus flange or tab.
I need to be able to dial in the chamfer after the part is created, yet maintain a crisp flat. I don't know how to do that in Sync. Only ordered maintains the flat sketc for editing later. If I tried to edit that later in Sync, I would no longer have a crisp flat. If I directly edit the flat pattern, the dimensions I need to dial in for the finished part are not available or shown.
My other big problem with sheet metal design are holes though 2 way and 3 way corners. And the single largest problem there is that I want a hole just a bit larger than the thickness but much smaller than the bend radius. Once the hole get's to that size, it is displayed wrong preventing me from manually turning the 3 way corner hole into a slot. This part of the problem is compounded by the issue of how normal cuts work (not relative to K plane) and that cuts not centered in a bend just don't work right.
Sync in general lacks any connection to flat patterns. Only flange lengths and bend location determine the flat. I typically work with a fixed piece of steel, then have the bend location float to match other things going on. Saves a lot of scrap.