I guess it's a holdover from when I used Linux more often, but for most applications it seems sensible to just let the WM manage tabs. I guess there are a couple of situations when that approach is worse, though:

- Tabs need to communicate with each other, or with a "host" application. In-process communication might be simpler than inter-process.

- Some people have WMs that don't provide an acceptable tabbing interface, and you want your application to have an acceptable interface everywhere. In this case I guess I'd suggest distributing a separate tabbing program along with your app, but that kind of separation of responsibility has definitely gone out of fashion.