That would not be obvious to me. I often have to process quite large and messy XML files and a functional approach works well. I'm not even sure how inserting print statements would be helpful.

There may be far better ways of doing it, but for a Haskell beginner (and I'm certainly one of those), being able to quickly display what each function was seeing as its input/returning as its result as it chugged through a complex file would have made life a lot easier for me when I first tried this kind of parsing in Haskell.