Yeah, the worst case of ghc's garbage collection is awful and can dwarf the actual work being done. That's the man driving factor behind adding linear types to haskell - they let long lived and large data live on a separate non-gced heap.

The other big part of this is that it can make stream fusion predictable. Currently haskell programs can become 100x slower or faster after some innocuous change, so linear types will make it a lot easier to write fast haskell in general.

http://blog.tweag.io/posts/2017-03-13-linear-types.html