Jerry Zhang [off-list ref] writes:
Unrelatedly would you have context on why --3way falls back on 3way
rather than trying 3way first then falling back on apply_fragments if
blobs don't exist?
Historical accident, following the order in which these features
were invented, plus applying a single patch straight has been faster
than doing a 3-way.
I tend to agree with what you are hinting at, though, as I do not
offhand think of a situation in which a successful 3way merge would
be less correct than a straight patch application, and if the user
explicitly has told us to do "--3way", that is a sign that it is
acceptable to try 3way first even if it costs more cycles.
Those who has been giving "--3way" from inertia would notice if the
performance difference is large enough and may complain, though.