Implementors of intermediate caches (proxies) have found it useful to convert the media type of certain entity bodies. A non-transparent proxy might, for example, convert between image formats in order to save cache space or to reduce the amount of traffic on a slow link.
alwaysAddNoTransform is true (it is false by default),
Polipo will add a ’no-transform’ cache control directive to all
outgoing requests. This directive forbids (compliant) intermediate
caches from responding with an object that was compressed or
transformed in any way.