SOFF -> Unlock of all partitions ..thus you can modify any part of software of your Phone
PROS:
1. gives you complete freedom ..you can literally tinker with any thing
2. Its like a door to Heaven ..i mean you can enter the custom ROM world ..and by flashing a good custom rom ..you will indeed have
performance improvements
CONS:
1. Easier to brick ..as you have unlock on every partition ..one wrong step in firmware flashing (low level drivers )..you might potentially
have a brick in your Hand ..but this can be easily prevented ..by being careful while flashing firmwares(verifying md5's before hand )
..and following the instructions properly
SON -> completely LOCKED ..you cant even root and will be stuck with stock ROM
SON with HTC-DEV unlocked bootloader -> unlocks system,boot,recovery and data partitions
PROS:
1. Gives you the ability to flash custom roms of same version
meaning ..if you do HTC-DEV unlock over stock ICS then you can flash any ICS/JB custom ROMS
and if you did HTC-DE unlock over stock GB (2.3.x) then you can flash custom stock GB ROMS
2. Little bit secure i would say ..so hard to hard brick this one ..as all the important low level software partitions are locked
CONS:
1. The Custom ROM flashing process is little bit different for this case (check asskickars guide on "flashing ROMS with SON " in
sensation general section )..and some times you might need to do some extra steps to boot the custom ROM
2. You cant change the RADIO and also cant flash firmwares ..which might help in getting better signal (not always true )
hope this covers up your questions