If you want to create Universal Binaries, then 10.3.9 is the minimum system platform, because this is the oldest OS version that supports UBs.
Intel-only versions of your software require 10.4.4 or higher; there has never been a (released) Intel-version of older OS X builds.
10.3.8 or older therefore can only support PPC-only software builds.
Personally, I do not believe that there are still many relevant (in terms of market share & interest in buying new software) Jaguar 10.2.x installations out there. However, if you want to support a by now five year+ old OS, you just have to get yourself at least one old Mac with 10.2.8 installed on it and test your software on that machine for compatibility and performance.
Jaguar was the first really usable release of OS X, but it still had many issues that only got resolved with Panther, and I think the Mac community knows that and most users upgraded to Panther or now even Tiger.
In my opinion, supporting 10.2.8 is a wasted effort, but that is just my opinion and if you have good reasons to support Jaguar, by all means, do so and test your software on it.
Intel-only versions of your software require 10.4.4 or higher; there has never been a (released) Intel-version of older OS X builds.
10.3.8 or older therefore can only support PPC-only software builds.
Personally, I do not believe that there are still many relevant (in terms of market share & interest in buying new software) Jaguar 10.2.x installations out there. However, if you want to support a by now five year+ old OS, you just have to get yourself at least one old Mac with 10.2.8 installed on it and test your software on that machine for compatibility and performance.
Jaguar was the first really usable release of OS X, but it still had many issues that only got resolved with Panther, and I think the Mac community knows that and most users upgraded to Panther or now even Tiger.
In my opinion, supporting 10.2.8 is a wasted effort, but that is just my opinion and if you have good reasons to support Jaguar, by all means, do so and test your software on it.