I've been rooting my Android devices for a long, long time without any problem, until now.
I installed a ROM that didn't agree with my N7100 and needed to get my phone back into a working state. Having only Macs at work meant I had to use Heimdall rather than the Windows-friendly Odin. Heimdall isn't quite as easy to get to grips with and couldn't handle the factory images I was throwing at it, so in a desperate attempt to fix this, I inadvertently deleted all of my EFS data...
...and I hadn't taken a backup.
A local 'backstreet' phone shop couldn't fix it, and Vodafone charged me £100 (as I'd invalided the warranty) to replace the motherboard.
So it's not only a silly mistake to make, it's an expensive one, as this 'experienced' rooter discovered
Whatever you do, never, ever delete, re-partition or reformat the EFS partition on your Galaxy Note II!
You have been warned!