Many editors like to use the timeline for organization. This is closely associated with Premiere and the "pancake" method of stacking timelines and editing between these sequences. However, organizing primarily in the timeline and not in the browser is something many FCPX, Premiere, and Media Composer editors do.
When FCPX first came out (10.0) you could skim through projects and view "filmstrips" of the various projects in the project browser. This function was lost with 10.1 when the Library came into being.
While I'm not advocating for stacked timelines in FCPX, I do think it would be a valuable feature to be able to editing directly from one sequence (project) in the browser to another in the timeline window. In order to do this, you would need to be able to have the "filmstrip" view of project restored.