There was one evening where I was confused because I was building improper lists and they were causing problems because I had no idea what an improper list was or why the cons operator seemed to be appearing randomly in my lists. Once I knew what they were and how to avoid inadvertently creating them it was not a big deal.
This article and the follow-up to it give some good insight into why iolists and the fact that improper lists work as iolists is very helpful at times. Phoenix make liberal use of this as the posts explain. I have a library that generates SVG and I can attest to how incredibly convenient this feature of the language is for building up a big sequence of strings.
