When making caramel candy the recipe often calls for boiling a water/sugar/butter mix to one temperature, then adding cream and boiling to another temperature. Often the second temperature is higher than the first. I assume the second temperature is set to get the proper amount of water driven off and the proper caramelization of the sugar. What is the purpose of the first boiling? How would the result be different if we just mixed the water/sugar/butter/cream and boiled to the second temperature? If the first one is higher I can see we get more caramelized sugar that way, but if the second is higher I don't see the purpose.
When caramelizing sugar in a recipe that uses water your first job is to get the sugar to completely dissolve. That is the first temperature you are using. They are probably making you pause at this temperature long enough to make sure you do this tep correctly. If they didn't have the step most folks would blow past it, add more ingredients and run the risk of not dissolving the sugar correctly.
Make sure no sugar crystals remains at the first stage, even on the side of the pot. If any crystals remain or fall in later your recipe will fail because the sugar will recrystallize leaving a grainy taste.
Caramel and other candies like toffee start off with a small amount of water and are brought up to around the boiling point of water and held there briefly (typically a couple minutes) until the water is boiled off (which then allows the temperature to rise to the desired sugar stage). The reason for this is that when sugar is heated in the presence of water it undergoes a slow reaction called hydrolysis where the sucrose breaks down into fructose and glucose (this combination of fructose and glucose is referred to as invert sugar). Invert sugar impedes the crystallization of sucrose and helps produce the desired texture of the candy. Alternatively, invert sugar can be introduced to the recipe to reduce the time spent at the first boiling stage or skip it entirely. High fructose corn syrup is a common source of invert sugar used for this purpose in many commercial candy operations.