ports-wide config caching questions

[fgudin at nerim.net]

Hi ports gurus !

Learning about autoconf, it made me think that perhaps my 486 (!) would
benefit much from having a rather persistent config.cache for the whole
ports tree. Googled a bit about it, to nothing much interesting...
Hence my questions to you, my friends : 1st of all, is it wise, i.e.
there will be times when a cache reset will become necessary, how to
determine it ?
2nd part : didn't see any knob for this is our .mk, do you see anything
else i might try to achieve this ?

Thank you very much for any help.

Francis.

PSE CC: me as i'm not currently subscribed to this list.