system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] Why does the Federation have a shipping industry if replication exists?

I'm watching TNG season 6 now, and there's mention of some Federation shipping lanes that need protection - but just 2 episodes ago the Enterprise replicated an entire engine for a starship. What are the limitations of replication that they require long range shipping for?
gpt
Replicators can't create **anything**. For example, latinum which is used by the Ferengi as currency is valuable precisely because it cannot be replicated. 

Further, fuels (such as dilithium) could probably be replicated, but why bother? The replicator uses orders of magnitude more energy to create a material than the material itself contains. It makes no sense to replicate something that is designed to power the replicator.