One of the reasons for Samsung's successful smartphone businesses is Google's Android. Sure; Samsung had smartphones before they adopted Android and created the Samsung Galaxy range of Android-powered smartphones. The Samsung Jet is an example of a successful smartphone that sold well before Android graced Samsung hardware, however after the business adopted Android, so things really started taking off. However, Android is not the only operating system that Samsung has used on its smartphones. In addition to their proprietary operating system on early generation hardware such as the Jet, Samsung have also used Windows Phone, Symbian and their own in-house operating system, which was originally called Bada and has been moulded into Tizen OS.
Tizen is shaping up to be Samsung's push into the Internet-of-Things and all number of smart and wearable devices, anything from watches (such as the Samsung Gear S2 smartwatch) to fridge freezers, including smartphones and perhaps at some point, tablets too. Comparing Tizen to Android, Tizen currently has a lighter footprint and so on like for like hardware, should be quicker or at least more responsive and use less power. This would make it perfect for the simpler wearable or smart devices, where processor power and battery capacity is at a premium inside small, svelte chassis designs. Tizen could also have a place in a smartphone, where hardware resources are also similarly constrained and notwithstanding the lack of third party applications for the smartphone Tizen OS platform, Samsung's early Tizen handsets make a respectable case for themselves. However, there is currently one significant flaw in Samsung's Tizen execution - the Tizen OS powered Gear S2 is not compatible with the Tizen OS powered Z1 and Z3 smartphones. Currently, the Samsung Gear S2 is compatible with Android devices and Samsung are believed to be building in compatibility with the iPhone 5 and later running iOS 8.4 and later, but this is not yet ready.
There are a number of theories as to why the Gear S2 isn't compatible with the Tizen smartphones. The Gear S2 has not yet been released in those major markets for the Tizen devices, which is perhaps not surprising as the Z1 and Z3 are currently on sale at the lower end of the price range, concentrating on the sub 100,000 won (under $87) market in developing smartphone markets such as India and Bangladesh. It's possible that Samsung are in no hurry to incorporate compatibility between the devices until such time as they are ready to release a high end Tizen OS smartphone, and even then it's unclear if compatibility will be enabled for older devices (although it would be strange if it was not). As such, there is no sense of urgency around building in compatibility between the two families of devices. In the past, Samsung's smartwatches were only compatible with the higher end of the Samsung Galaxy line of smartphones.