This can be very useful for a stealthy type of 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.
Concerning the previous two pieces of advice: ensure that you do NOT have any attack mods installed (like Revenge). Shade can break a cloak if he attacks.
Shade tends to cloak as Nyx is using her ultimate, so it is recommended to choose another sentinel if you plan to use 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. Tested on 5/21/15, ghost does not uncloak if the melee attack does not connect. This was tested only using the dual ether.