Lazy evaluation does make understanding performance/memory behavior hard, but usually you'll be using pipes/conduit/machines instead of lazy lists in production

Lazy evaluation does make understanding performance/memory behavior hard, but usually you'll be using pipes/conduit/machines instead of lazy lists in production code, so its not much of an obstacle for real-time behavior. However GHC's garbage collector can be an issue for real-time code, having high 99th percentile latencies.