Under price instability, there is less growing back after the slaughter since the credit structure is in such chaos. With price stability, liability production is much calmer while a large failure is occurring like an LTM, allowing everything to move smoothly.
But what is that notion of price stability ?
After all, if we include in the price basket, everything that is bought with money, including "store of value", then with a constant amount of money, by definition we have price stability. You only get price fluctuations with "sound money" if you leave out part of what is bought with it.
The price stability of a regulated money is only the stability of a certain basket, putting all the fluctuations in the complementary basket (usually speculative products, and store of value).
If you take the monetary formula, P x Q = V x M, then all the price fluctuation comes from the fluctuation of V with sound money (M constant).
The point is that Q is only part of the economy: the other part is "store of value". Now let V be precisely the "inverse of store of value": the higher V, the lower the demand for store of value (the lower the price of store of value).
So if you take the TOTAL economy, namely Q AND "store of value" then the price of that basket will only depend on M.
This is why sound money gives total price stability, and that the "price fluctuations" you observe are nothing else but price fluctuations between sub baskets, because they are related to changing offer and demand, which is exactly the price signal.
It is because one excludes the "store of value" aspect of the economy, that it seems that prices fluctuate. By wanting to keep the price of a part constant, you increase the fluctuations in th "store of value aspect (also called "blowing speculative bubbles"). We have seen that with the dot-com bubble, with the housing bubble, and with the banking bubble.
THAT is the result of your "price stability". You blow bubbles in the part that is not in your basket.
EDIT: let me illustrate that with a toy example.
Suppose that there is 100 credits in circulation and that at a certain point, the velocity is 2.
That means that in general, there has been bought for 200 credits, and that the demand for store of value is 50 credit-years (on average, the 100 credits are held half a year).
Now, suppose that the next year, the velocity is 1. That means that there has been bought only for 100 credits (deflation!!). If Q is constant, we have a deflation of a factor of 2 ! Help ! Price instability !!
But no. In the mean time, it means that the demand for store of value has increased from 50 credit-years to 100 credit-years.
So although in the Q-basket, the price has lowered by a factor of two, the demand for store of value has doubled. People have preferred to buy "store of value" instead of goods and services. If you would have included the demand for store of value in the calculation of ALL the demand, then both balance out. The economy is not just Q. It is also "store of value". That's part of people's demand, but doesn't show up anywhere (only in V). So the basket simply shifted, from more Q and less store of value, to less Q and more store of value. The price for Q and the amount of store of value are the signals indicating this change in aggregate demand.
If you want to keep P constant (which is the sub basket containing only the aggregate demand for goods and services, excluding the demand for store of value), then you screw up the market signals for "store of value", which is typically where a central bank fucks up.
Keynesianism is exactly based upon that notion: that we have to screw up the market for "store of value", because for Keynesians, storing value is a Bad Thing. However, it is part of people's aspirations, of their demand, of what they value. Keynesians start from the (correct) observation that the demand for store of value fluctuates and that this would lead, if unhampered, to price fluctuations of the aggregate demand (goods and services). As Keynesians want people only to want goods and services, and deny them their right to want to store value (or to change their demand for store of value) they try to play with the store of value so as to counter act the people's demand fluctuations: if there is a lot of demand for store of value, which would lower V, lower prices, and increase interest rates, Keynesians devaluate money by printing some, to make the store of value in money unattractive, lower interest rates, and cause inflation.
On the other hand (although rarely done in practice) if people want to lower their stores of value, and spend the money, strict Keynesians would destroy money, make store of money more attractive, and increase interest rates.
As, however, nobody is stronger than the market, people try to find other ways to store value, which gives rise to a huge financial sector, which mainly exists to try to counter act the market distortion imposed by Keynesian denial of the fluctuating demand for store of value, and the doctrine of constant prices of goods and services.
This puts in place the machinery to blow speculative bubbles.