What is this about?
If your device is caught in a force-close loop after booting (i.e. some app starts, the "force-close" dialog appears, you hit "close", it starts again -- and this cycle is never-ending), Safe Mode is offering you a remedy: A lot of things otherwise automatically started once the boot process is finished won't start in Safe Mode, so you can e.g. easily uninstall this misbehaving app.
Note, however, that some other functionality might be unavailable in Save Mode as well -- so it's obviously not a good idea to permanently run in Safe Mode.
Useful related questions on our site
- What is safe mode?
- How do I enter the Safe Mode on a HTC Desire?
- Is it possible to Boot into Safe Mode on an Android Device as a Precautionary Measure If Required?