Sorry, when I said new data structures, I meant containers like maps and list, which I very rarely get to create day to day.
I can see it for your transformations, but I have seldom seen cases where generics would really help (usually we're talking about comparing complex structure types that will need custom code anyway).
"Theorems for free"! By which I mean, when I'm coding something and it could be universally quantified on the type, then it's better to do so. That way, it's impossible to phrase certain errors. For example, a function `Set<a> -> Set<a>` must produce a subset of the input set; that's guaranteed by the types. I can't accidentally include the value 0 in my set, because 0 isn't of that generic type. The generic forces you to think in terms of the structure you're manipulating, rather than in terms of its contents.
I can see it for your transformations, but I have seldom seen cases where generics would really help (usually we're talking about comparing complex structure types that will need custom code anyway).