*.profile file changes in regression tests?

[Adam Spiers]

I'm starting to get the hang of regression tests, but my
build/out/test-results/index.html shows a very large number of entries
referring to *.profile files.  I assume this is something to do with
performance, but for once the Contributor's Guide isn't much help;

http://lilypond.org/doc/v2.15/Documentation/contributor-big-page.html#precompiled-regression-tests

says:

    Profile files: give information about TODO? I don’t know what they’re for.

How do I know whether I should be worrying about these?  And is there
a way to just see the images?  They are currently buried under
hundreds of these .profile regressions, so they are a bit hard to
find.