Functions should be short and sweet, to an extent, because by thinking in terms of functions you're building a new language in which you write your program.

If you're writing big functions by habit then you're just laying more code after existing code to build a program. If you split your code in functions and, instead, start talking in the language you've just invented then you're composing a program. And I think compilers should do the building while I refrain myself to composing.

Of course, one-line functions don't have inherent value but sometimes they're needed. For example, to present a higher-level concept that just effectively happens to be a simple assignment or an inc.

Short functions themselves don't have an inherent value either: if you manage to write your function with less tokens, possibly due to composing it out of other functions, then that's all good but isn't the real value of doing it. Shortness for the sake of shortness only matters until you're down to a screenful or so.

The real value of defining and writing functions is thinking of the proper words for your language. As soon as you're making your own language, then you're just using functions as vehicles to represent words in that language. Some words might take 30 lines to code, some words might take 3 lines. It doesn't matter as you've got your language together in a way that is concise and beautiful which is the real point.