I've had many cases in the past (not in go) where I've had to make use of that exact same function (in typescript, in F#, and in C#). it is actually quite useful when doing any amount of data manipulation (map/filter/reduce chain that often ends up into a list of key-value pairs, which then get turned into a map/dictionary of sorts).
At least in my job(s over the years), turning a flat list of db records into a more complex, nested (potentially on multiple levels) data structure before handing it off to the front-end is a very common. I've seen it done with "simple, fast code" (although not in go specifically, but in other languages), but it very quickly turned into huge messes of of long nested for loops and was very difficult to read. LINQ, Lodash, java's streams... I sincerely can't understand how go developers live without them. They make me a lot more productive both at reading and writing the code.
At least in my job(s over the years), turning a flat list of db records into a more complex, nested (potentially on multiple levels) data structure before handing it off to the front-end is a very common. I've seen it done with "simple, fast code" (although not in go specifically, but in other languages), but it very quickly turned into huge messes of of long nested for loops and was very difficult to read. LINQ, Lodash, java's streams... I sincerely can't understand how go developers live without them. They make me a lot more productive both at reading and writing the code.