To effectively use steam for baking bread, one needs to understand the related physics. One cannot guess, as much of what happens defies intuition, and guessing can easily be off by orders of magnitude.
First, prepare a list of relevant questions: How much energy does it take to melt ice, raise the temperature of water, or turn water into steam? What happens to that energy when steam condenses back to water? What is the volume of steam produced by a given quantity of water, and how does that compare to the volume of one's oven? How much heat energy can be stored by a given mass of metal or stones, and how does that compare to the energy required to heat a comparable mass of water?
If you are not absolutely sure of the answers to these questions (as sure as our predecessors were that the first atomic test wouldn't ignite the atmosphere) then begin your research with a period of peaceful meditation, ridding your mind of preconceptions. Compared to science, cooking is more prone to accepting authority and propagating group think, which can often be wrong. Learn peaceful resistance to ideas propagated by authority. One has spent a lifetime observing people spritzing ovens with a plant mister, little more than genuflection. Rid one's mind of the preconception that this works.
The idea of using ample steam at home was popularized by the Bouchon
Bakery cookbook, though it can be found in earlier professional sources. 350g
of water will produce enough steam to fill a home oven or an outdoor ceramic barbecue cooker several
times over. In contrast, a few spritzes from a spray bottle will be 10g of
water if one is lucky.
It takes 80 calories to thaw a gram of ice, 100 calories to bring that gram to
the boiling point, and a whopping 540 calories to then turn that gram of water
to steam. By weight, steel holds about 13% as much heat energy as water. These
numbers explain why one needs so much metal to boil the water, and why it
hardly matters whether the water starts out as ice or hot water.
For example, to turn 350g of cold water into steam, using metal heated to 450 F (132 C above boiling) takes about 28 pounds of metal. To turn ice into steam (giving one a slower fuse) takes about 32 pounds of metal. I accomplish this by filling a giant cast iron skillet with two spools of stainless steel chain. Indoors, I quickly but carefully pour water from a metal hiking water bottle, wearing gloves and standing back. Outdoors in a Komodo Kamado ceramic barbecue cooker, I use a slab of ice frozen for this purpose, to buy extra time setting up.
What does the steam do? It isn't simply keeping the crust damp, or one would far more easily spritz the dough. (In grade school a teacher tried to tell us that candle wax slowed down the burning wick; similar skepticism is called for here.) The dough is the only thing in the oven cold enough to condense steam back to water. The energy used to turn water to steam is delivered to the bread as the steam turns back to water. Physics abounds in conservation principles, and this is one: The energy has to go somewhere. As a thought experiment, imagine bashing the bread with a baseball bat, with all your force. Then imagine spritzing with a plant mister. Trust your intuition; which is more force? As a second thought experiment, imagine spritzing your bare hand and sticking it into the hot oven for a few seconds. Now imagine sticking in your bare hand as you turn 350g of water into steam. In which scenario do you then imagine a visit to the emergency room?