In reply to MikkelF:
Unless you're (very) fast, you will end up bivvying on a long route. It's just a natural thing to do. Preferably planned as well! If you've done TDs without bivvies, you've either been light and fast or you just haven't done long enough routes.
Some route's I've bivvied on around Cham - Walker Spur, Bonatti Oggioni on the Brouillard, South Ridge of the Peuterey and Chamonix Aiguilles Traverse. All fairly long routes but of course they've all been done in a day by people who are faster, fitter and better!
Whether to take bivvy gear or go light and fast (or at least light...) will depend on the route and your ability, as well as the time of year and the terrain.
For example, when we did the South Pillar of the Barre des Ecrins, it took us a 25 round trip from the car park. We hadn't taken bivvy gear and just carried on through the night. That made sense as we had reached the top of the difficulties just as it got dark and then reached the easy snow slopes on the descent by around midnight - the next five hours was just a fairly easy but long walk out and we wouldn't have bothered stopping even if we had bivvy gear. Actually we had hoped to do it in about 18 hours as that's what a couple of friends had managed. We knew it could take longer but not so much longer as to require bivvy gear.
Whereas if you're going to have to stop while you're still dealing with technical terrain or a complex descent, it makes sense to take bivvy gear, recognising that you will be somewhat slower overall.