I heard this once in the context of an explanation of Matthew 15:27, where a woman says to Jesus, "yet the dogs eat of the crumbs which fall from their masters' table." The person doing the explaining said that bread was so cheap and plentiful at that time that it made economic sense.
The idea that this verse refers to "pieces of bread used by the guests to wipe their hands on and then thrown to the dogs" seems to have come from the commentaries of Richard Chevenix Trench, but the "Cambridge Bible for Schools and Colleges" refutes this interpretation (reference is just past halfway down the page), and most commentaries seem to take this at face value and assume it is literally talking about crumbs/scraps falling from the table. I found that reassuring.
However, Google suggests that this was a common practice in Ancient Greece. People would use apomagdalia, the soft bread inside the crust, to clean their hands. I found that un-reassuring.
The idea has always bothered me, because I can't help thinking of the people who made the bread. Considering how complex bread production must have been in a pre-industrial era - growing and harvesting the wheat, separating the wheat from the chaff, grinding the wheat into flour and making the flour into bread - was it really economical to use bread as a napkin, or was it evidence of decadence, only for people who could afford to waste food?
Thanks in advance!
The idea that the apomagdalía could be used to wipe hands is reported explicitly in Aristophanes, Knights 415, and is implied by the word itself, since apomass-, apomag- means 'wipe off'. This isn't copious evidence, but the fact that the word literally means 'wipe-off-stuff' is conclusive.
The idea that the apomagdalia is also given to dogs is also reported in the Aristophanes passage --
Sausage-seller. ... or it would be in vain
that I was reared feeding like this on apomagdalia.
Paphlagonian. On apomagdalia? Like a dog?
as well as in Alciphron 3.8 ed. Schepers (3.44 Meineke) and Plutarch, Life of Lykourgos 12.
So Trench's interpretation is unobjectionable on that ground. Whether there's any connotation in Matthew 15.27 of this use is another question; the word that the Canaanite woman uses is psichia, 'crumbs', which could be any small morsels of food, though Jesus' reference to 'bread' in 15.26 certainly points towards pieces of bread in 15.27 too. Still, Trench's basic point that 'wipe-off bread' was one of the kinds of things you could feed to the dogs at dinner is rock-solid.
So the remaining question is about the economics of bread-making. Peter Garnsey, in Cities, peasants and food in classical antiquity (1998), p. 229, reports that in Rome in the principate era, a large proportion of the population was given a grain allowance of about 33 kg of unmilled wheat per month. Here's an unreliable report that 1 kg of unmilled wheat produces about 840 g of finely milled flour, or 975 g of wholemeal; and bread is typically about 1.6 times the mass of the flour in it. So 33 kg of unmilled wheat translates to about 50 kg of bread. Garnsey reports (citing various sources) that it would take 650-800 g of wholemeal bread per day to meet 100% of an adult's energy needs, eating only bread and nothing else. That works out to 19.5 to 24 kg per month. So the basic free allowance in Rome would more than meet all the energy (and protein) needs of two adults.
Now, these allowances were presumably intended to feed entire households, but then again, it would be an extremely poor diet to live entirely on bread, and only the completely impoverished would have to rely on this allowance for more than 75% of their energy needs. Diets presumably varied in different parts of the ancient Mediterranean, but again on the other hand, barley and wheat were the mainstay of ancient Mediterranean diets pretty much everywhere.
The long-and-short of it is that bread was available in copious quantities, and it seems beyond doubt that it was used for 'wiping off' (the literal meaning of apomagdalia). As a result I don't see any objection to Trench's interpretation.