It is very rare that I don’t have a project with multiple timelines. I would ask how it might be possible to manage most work flows with a single timeline. Apart from the most simple of jobs I have never managed that.
Here’s a typical job workflow from my perspective as a colorist finisher of an edit. Import XML/ AAF. Check timeline to match all shots. Duplicate timeline so I can always reference back to the ungraded editor original. Grade pass in new timeline. Once grade is locked then work on titles & supers. This may be another duplicate of the grade timeline so I have a text and textless version. Edit the deliverables which may be up to nine or ten edit variations of the program as dictated by the broadcasters world wide. Each one is a new timeline so that all is contained in the one project. So at the end I may have 12 or more timelines depending on how many variations for delivery are required. This is typical for a simple documentary.
If I then had to create various language subtitles then the number of timelines will increase. Swapping between projects with single timelines would drive me crazy. It is so much better to have everything in a single project with multiple timelines so when all is ready, I can create a nice big render cue in that project and let the computer go overnight creating all the variations of the program.