USB debugging enables adb.
The device itself runs adbd and debuggerd, these are different processes for different purposed. adbd handles adb shell etc, so is usefull to keep running. Otherwise you'll be really stuck if something broke!
debuggerd is used by the SDK debugger. It shows debug information for your test process. Unless you're developing apps you dont need it. And if you do one day, just adb in and rename it from debuggerd.off back to debuggerd
If you're developing apps you should be running a stock system anyway!
so debuggerd is useless for most users, and those that need it should know not to run that line
