What is safe mode?

My USC "Desire" locked up the other day. I have Android 2.2 installed. It just kept rebooting to the splash screen over and over and over again. Being an old Mac user I thought some "key command" might get it to stop. So I tried holding the HOME key as it booted, brought it to "safe mode". Ane more reboot and it was running again. Is there a log I can look at to see what the issue may have been? What else can one do in "safe mode"?