Documentation for cachetime at
http://www.dokuwiki.org/config:cachetime says
"Set to -1 to turn off the cache."
However, cache files are still written to data/cache.
Implications:
a. Performance
b. Unintuitiveness
c. More importantly, if caching is turned on in the future (by setting cachetime to a value other than -1) the existing cache files in data/cache will be used, which may be outdated.