This can be turned on and off on a per forum base and for categories of the resource manager.
You can style the tabs, if the default is not fitting to your style.
And you cann de/activate special tabs and the display if empty tabs should be showed differently.
If you enable the empty tab option, one additional query is added. But usual this query should not slow down your site. But if you have a huge forum and there are no empty tabs, you can save this time.