Just like local environments you may not run ask https etc. if you needed to trouble shoot sessions why would you encrypt them so you can't read them? Also if your storing sessions server side in an inaccessible folder why would you hash them just to unhash right away?
Encryption is useful is you're using external storage for your sessions (Redis, Database, etc). There's always a chance it could be intercepted when it's transmitted. If it's encrypted, it's less of a concern. However, good encryption is always CPU intensive. It might not be an option if you have, for example, an API endpoint that is under high load and is required to respond quickly.