Expected performance benefit of using a non-file CacheMethod (Redis, Memcache)
As with most performance related questions, the answer is "it depends". :)

Apps like Redis and Memcache store their key => value stores in memory as opposed to disk-based file caching.

Accessing data from memory is usually orders of magnitude faster than accessing data from disk.

All of these fall under "General purpose data caching" and Craft will use them internally for its own operations and plugins can certainly make use of them as well.

If you have a plugin that makes extensive use of data caching and/or you've got a heavily trafficked site, then you will likely see some tangible performance benefits.

If you're just doing a basic stock Craft install on a low trafficked site, then you likely won't see much of a difference at all.