Andreas Krey [off-list ref] writes:

A short trial showed that representing first parent chains as
straight lines in the graph does actually improve understandability,
as feature branches clearly stand out as separate lines even when
they no longer carry a branch name.

If you have a four-commit segment in your commit ancestry graph
(time flows from left to right; turn your head 90-degrees to the
right if you want a gitk representation):

    ---A--X
        \/
        /\
    ---B--Y

where X and Y are both merges between A and B, having A as their
first parent, how would you express such a graph with first-parent
chain going a straight line?

Also, there is an implication with 'git pull': You'd expect the
master branch to be a first parent line, but when I do a small
thing directly on master and need to pull before pushing back,
then origin/master is merged into my branch, and thus my side
branch becomes the first parent line.

Don't do that, then.