Is the scarf joint done on the plywood before cutting to dimension, or after?
In one case that would reslt in a 16' length that is then cut to dimension.
In the other case, it would result in two cut pieces being lined up and joined after cutting.
Is one better? Considerations?
You are working from plans? Yes? Not a kit.
Join the full length, then draw your shapes and cut them out.
You have the chance of misaligning your pieces, or having them slip, if you epoxy glue a scarf after you cut the pieces. In addition you don't have to remember that there is a loss of dimension at the scarf overlap.
...agree, with the caveat that pre-scarfing pieces that are pretty close to your final shape can save a lot of material. Doing this saved a full sheet of ply on each of the CH17's we built, for instance (I also built pattern/templates first, so gluing odd shapes over the templates was just a matter of making sure the pieces fully overlapped/covered the template).
Your choice where you want to go on the risk-reward spectrum.