Functions are not usually as obvious as the creator thinks they are.
Does get_height() include the optional border width or not? What does it return while the item is hidden? Does it return an int or float? Can it return a string value like "auto" or a null value? Under what circumstances should its value not be relied upon, e.g. while an animation is active? Why was it written as a function rather than a property? And so forth.
Requiring a comment is helpful in reminding the author to explain why this code was even separated out as a separate function in the first place, and all of the potential gotchas around it.
Does get_height() include the optional border width or not? What does it return while the item is hidden? Does it return an int or float? Can it return a string value like "auto" or a null value? Under what circumstances should its value not be relied upon, e.g. while an animation is active? Why was it written as a function rather than a property? And so forth.
Requiring a comment is helpful in reminding the author to explain why this code was even separated out as a separate function in the first place, and all of the potential gotchas around it.