[lgas]

Honestly, pretty much never, but the stuff I work on these days does not have significant performance or scalability requirements so usually I just write the most straightforward code possible and it's fast enough and doesn't leak.

The only place I really ran into that was on a project that inherited a framework written by consultants and that was really due to problems with the framework and not the language. Though I do still cargo cult some practices from those days that may be helping me to avoid some pitfalls today without realizing it -- eg. almost every field of almost every run of the mill business-domain data structure I create is strict (eg `!Int` instead of just `Int`).

I imagine you're going to hear more of the horror stories on the internet than the successes, but that sort of thing can be legitimately frustrating when coming to Haskell from other languages just because a lot of what you know goes out the window and you have to learn new concepts from scratch while getting up to speed on a new language with a new tool chain, etc. At some point you make it over the hump and it largely becomes a non-issue.