Although it’s described as Caseta support it’s really Lutron SmartBridge support, and Lutron has been adding more models to that, including RA2. But not all devices have made it into the smartthings integration, so it does get complicated. Not even all Caseta models.
For example, the Caseta fan switch has been out for over a year now and is supported by most home automation platforms That support the Caseta dimmer switches, including Hubitat. But it doesn’t work with the smartThings integration. Lutron support says it’s up to smartthings, smartthings says it’s up to Lutron, and it appears that no one is working on it. 
HomeKit or anything a consumer has control over make use of the Pro features?
HomeKit can work with either Lutron bridge model as long as it is the second generation.
The main difference in the pro is that you can use telnet with it, and it has an open API.
There is an unofficial community-created integration with the pro model which lets you use Lutron pico‘s With smartthings. (The Picos are invisible to smartthings through the official integration) . That does require setting up an additional device as a server, but it’s a good example of why a DIY person might want the pro.
[OBSOLETE] How to control anything with inexpensive Lutron Pico remotes
If you’re going to use Hubitat, which has an excellent lutron integration, that’s another example of when you would want the pro.
(Since the pico is the battery operated Lutron switch, I think that means all of this is still on topic for this thread, since which bridge you use will determine how you can potentially use the Picos with smartthings, although additional devices and set up will be required.)