SUMMARY On Kate, clicking on the option "Show Tabs" on the "Settings" menu changes between showing the tab bar or not, no matter the number of tabs open. On KWrite, the same option only makes effect when there are various tabs, because the tab bar itself is only shown in that case. This is confusing, because when there is only one tab (and thus, the tab bar isn't being shown) clicking on the "Show Tabs" option does nothing, the tab bar is already hidden and cannot be shown. Besides that, the necessity of the option itself is dubious on KWrite. The tab bar is already hidden when there aren't other tabs open, and it doesn't seem of much use hide it when there are various tabs, making the program harder to use (one can still change between tabs with a keyboard shortcut).
I think this option does what it should and is consistent with other applications. Yes, if you turn them off, it makes it harder to use with multiple files, but same could be said for hide menubar or hide toolbar.