Version: unspecified (using KDE 4.5.1)
A lot of applications like web browsers, file managers, terminal emulators on both GNOME and KDE use tabs in their interfaces. GNOME’s text editor gedit does too, and Kate does not. The document list is enabled by default, and is some sort of replacement for a tab bar, but it is inadequate: it consumes a large amount of vertical space, and also requires an additional click if it isn’t shown. Users also expect a tab bar based on the behavior of other applications, Kate shouldn’t ignore that.
Therefore I propose that the tab bar plugin be enabled by default, and the document list is not shown by default. I can’t imagine why anyone would prefer to use the document list, but with my proposal they could still disable the tab bar and enable the document list. For the majority of users the tab bar would be more beneficial.
Reproducible: Didn't try
We've had this discussion a lot of times. In short: A tabbar does not scale if you have e.g. > 10 files open. Many users use Kate for development and have even 40 or more files open. This is why the Documents list will stay, without further discussion ;) If you dislike the documents list, use a tabbar plugin.