So, this is not entirely an accurate problem. There was no "economic crisis" when Weimar Germany was printing money, neither was the French economy in particular trouble (political risk notwithstanding) during the Revolutionary period. What WAS problematic was government finances, or "fiscal policy." However, this was not always the reason for printing money, but we'll get into that in a little bit.

In the context of Weimar Germany, Germany had taken on the obligations of the Treaty of Versailles, including its reparation clauses that called for payment to Britain and France, both in the form of lost territory (Alsace-Lorraine to France, and the loss of Silesia and other eastern territories to Poland and other countries) as well as in material payment. Germany did everything they could to obfuscate the process, not because the reparations were particularly harsh (they weren't) but because the reparations were seen as shameful. To get rid of this shame, the Germans wanted to get rid of the reparations. This ranged from just being annoying (delaying scheduled coal shipments, for example) to being outright malicious, which is where the accelerated printing of the German marks fell into.

The reparations stipulated that the Germans needed to pay the reparations in a mix of gold and other things (such as coal). Since the German government only had limited reserves of gold, they would need to purchase additional gold using state funds to make up the difference. Now ordinarily a country would usually do something like raise taxes or borrow money in order to increase the amount of funds available to them. This is known as fiscal policy.

Fiscal policy is different from monetary policy, which dictates control over the supply of money (number of bills, what the backing is, etc.). While the study of monetary policy was still in its infancy, it was well known that debasing the currency would lead to hyperinflation. Despite this fact, the Germans chose to print money, reasoning that destabilizing their economy would make it more likely that the reparations could be renegotiated. Which they in fact were, during a renegotiation known as the Dawes plan, and later further renegotiated under the Young plan. Essentially, the Germans intentionally instigated an economic crisis for the sole purpose of ridding themselves of the shame of Versailles, which would only be healed by massive American loans and the establishment of a new currency backed by real estate, the Rentenmark.

In general, printing money was (and is) widely accepted to be bad for the economy. The reason governments chose to do so was entirely because there was an imbalance in fiscal policy (government spending vs. government revenues). However, some governments had less recourse to correct the problem than others. In the case of Revolutionary France, most banks were hesitant to lend money to this new, unstable government (not that the original French government was exactly creditworthy, but a sufficiently high interest rate will attract lenders), so borrowing money wasn't an option. Similarly, raising taxes would have done nothing but antagonized the populace, which the new republic depended on for legitimacy. At the same time, there was massive need for government spending-whether it be for military expenditure, government subsidy, public works, or just simple appeasing of the mobs-and the money had to come from somewhere. Some of the poorest people in fact supported inflationary policies as this would reduce the value of their debts. All things considered, the government really didn't have a choice but to print money (the number of assignats, which were originally government bonds but later became legal tender, grew astronomically over the revolutionary period), and thus had to endure the economic consequences while doing whatever they could to obfuscate the impact.

Sources:

The Myth of Reparations, Sally Marks
When Money Dies, Adam Fergusson
Stuff and Money in the Time of the French Revolution, Rebecca Sprang