[hotmetal]

I expect there will be differing views on this. Firstly, time isn't the final arbiter - taste is. Getting a shot in 25 seconds or whatever is only a guide. You've correctly realised that there's a relationship between dose and grind affecting shot time. But there will be a difference in extraction between a finely ground 14>28g @ 25" shot and a 17>34g also pulled in 25". If you prefer the results from the 14g dose, (or you can't taste the difference) then you might well be 'wasting' 3g of coffee if 14g is what you like. But they're not the same. Also, if you under-dose the basket too much, you are more likely to get channeling and gushers I would think. You can't just keep going finer and finer and use less and less coffee - but there's no harm in seeing how far you can go (and noting the taste difference and your % successful shots from a consistency point of view). Remember that as you reduce dose, you either get less coffee out, or you stretch the brew ratio to the point of bitterness (potentially, ristretto and lungo notwithstanding). That's my tuppennorth anyway! Hope it helps.