system
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human
In cooking, is the term "boiling" used because it's a nice visual baseline to know the approximate temperature of the water? Or is there something fundamentally important happening at water's boiling point?

When cooking, you're often told to bring something to a boil, then cook for X minutes, etc..

My question is this: is the term "boiling" used in the instructions because it's a nice visual baseline for cooks to know the rough temperature of the water? Is there something special that's happening at the boiling point that improves cooking? Or is it just hard to know the temperature of the water, and therefore waiting for it to boil is a nice way of knowing when the water/soup/whatever is at a specific temperature?

If it were incredibly easy to know water temperature while cooking, would we see recipes with more specific temperatures (ie, "bring water to 200ºF and cook for 10 minutes,") or is bringing the water to 212ºF (100ºC) somehow chemically important?
gpt
The boiling point is important not just because it's an easy way to know what temperature the water is (which was very important before it was easy to walk into a store and buy a fairly accurate thermometer), but also because it's a stable temperature (barring the drop when you first add food to the pot).  If you're trying to hold a pot of water at, say 180 F, you won't really be able to so very well, especially on a slow-responding cook top like electric, but really even on gas.  What you'll basically be doing is yo-yo-ing, or oscillating, around that temperature, and you'll probably have to turn the heat up and down or on and off (or on electric, take the pot on and off the burner), etc.  But because the water will not get hotter than its boiling point without, well, boiling, you can pump as much heat into the sucker as you want and, short of boiling all the water off, you don't have to worry about the yo-yo effect.

It's worth noting, though, that in many cases a simmer is a preferred method to a boil.  A violent boil throws around delicate foods, and generally the slightly lower heat in a simmer (it can range from 200 to just a hair under 212 at sea level) is kinder to delicate flavors and textures.  A simmer does, however, require a little more maintenance than a boil.  It's also worth noting that some recipes do call for prolonged cooking at a less-than-simmering temperature--for example, some poaching recipes (some call for a simmer, some call for temperatures as low as 160 F).  These recipes are often a pain for people who don't cook a lot because 1) you ought to have a thermometer and 2) it's harder to control the temperature here.