This can be very useful for stealth based gameplay.
Combining Ghost with slow and heavy hitting melee weapons can give you the edge, cloaking you as you get close giving you time to prepare your attack. (NOTE: See bugs)
Due to the cloak keeping your ability to recharge your shields, it is especially useful if you're about to die, cloaking yourself in the middle of a fight and not attacking will recharge your shields and keep you alive longer in high-threat situations.
Apart from supporting stealthy gameplay, Ghost can confuse a group of enemies if you cloak, and can save you from dying if used correctly.
Shade will not cloak their users if they are doing something that raises their aggro, sch as Nyx's Absorb.
The Shade can emit the Ghost effect endlessly without granting actual cloaking effects, by activating and deactivating this ability too quickly while firing weapons.
The Ghost ability will occasionally turn on without any enemies nearby to trigger it.
03/28/2014 - Ghost uncloaks when melee button is pressed, rather than when attack connects. This was discovered while using Scindo and not tested with other melee weapons. Proven on 06/06/15, ghost uncloak even if the melee does not connect, this was tested using Karyst and Skana. Jumping from high ground also uncloaks.