There currently isn't a published change log / release notes for sFlow-RT and it there was it would likely have generic "bug fix and performance improvement" comments since external APIs are stable and haven't changed in some time.
Each monthly release updates GeoIP database and dependencies on external libraries (Jetty, Rhino, Netty, etc) to keep them current. This drives occasional updates to the Java version (17+ for 3.2, 11+ for 3.1, and 8+ for 3.0).
In summary, you may want to keep to an older version if it is working well for you, particularly if you don't want to upgrade your Java version. New capabilities, like RoCEv2 / Ultra Ethernet decodes have been added recently. Documentation on sFlow-RT.com reflects the latest released version, so you can see if there are new features. New capabilities are also generally covered on
https://blog.sflow.com. If you need the new features or want a performance boost, then upgrade. It's always prudent to test a new version before rolling into production in case there is a regression. Please raise any issues so that they can be promptly addressed.