Sequencer & Preview
Figure 1 shows the combined Sequencer & Preview View Type. It looks very much alike the default Video Editing Workspace (but without the File Browser, Properties and Timeline editor). It is however only one instance of the Video Sequence Editor with the View Type Sequencer & Preview, while the workspace contains two instances. As a result the combi-view has only one sidebar and one toolbar with all the tools and properties of both view types.
Some users prefer working in this view because all the tools are available. On the other hand, the toolbar and sidebar occupy the whole screen and so, it is not possible to have the sequencer timeline full width without also hiding the sidebar and toolbar for the preview and vice versa.
It's also more difficult to add a small window. One common used technique in the workspace is to replace the file browser window (temporarily) with another editor, eg. dope sheet.
And of course, it's also not possible to have the Sequencer timeline or the Preview alone in fullscreen (Ctrl-Spacebar); eventually on a second monitor.