Thanks Bart,
If we are talking about downsizing the pixel dimensions, instead of reversible compression...
Yes, I had pixel dimensions in mind.
...there will be losses. Upsampling that result will usually not restore the losses...
Understood (except for your use of "usually" - how can it ever?). However, taking into account the competence of current software at upsizing, and that a significant increase in resolution is required to make a meaningful visible difference in a print, my thinking had been that although the final image would be less detailed, colour would be more accurate, and that this may be a worthwhile trade.
But it sounds like you lose more than you gain, except perhaps in extreme cases.