[GraphHopper] Understanding the impact of prepare.chShortcuts=fastest

[Ludwig]

To prepare routing files for more than one vehicle type at once, I have to
comment out

#prepare.chShortcuts=fastest

and then also in the Java code add

setCHShortcuts(false, false);

This setting for the generator creates significantly smaller routing files,
which is a good thing, but it disables the use of the contraction
hierarchies, which should slow run-time route generation down.

I have not actually measured the slow-down, but on the Android devices that
I tested it still feels pretty fast, certainly fast enough, particularly
when considering that the files get much smaller.

Are there any worst case scenarios that I should be aware of? Are there any
other trade-offs (such as larger memory use, inability to find certain
routes)? Is the impact of these settings bigger for larger areas (longer
routes) and less important for areas like individual cities with shorter
routes?

Ludwig
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