Full Disk Encryption is like buying new locks and keys to your condo so that there's no possibility any of your neighbors, friends or relatives can get in, just in case you once left a key under the mat or over the door.
But it is another of the strategies that can be deployed, especially in sensitive situations where "end points" can be compromised on mobile devices and physical locations that are unprotected physically.
Good to see someone has done the math so that reasonable prices for the technology can be determined.
Thanks to Network Computing - For IT by IT
Calculating the Cost of Full Disk Encryption - Network Computing