Nope,
It keeps them from screwing out when you remove the stud at a later date. The tab used to screw the the heli coil with the helicoil installation tool in is nornally snapped off so reinstalling the coil can't be done. It's a trick the more experienced guys do that's all, the guys that have actually seen the properly installed coils thread out. This is one reason why a threaded insert is better. Many a spark plug have been removed with helicoils attached 
You let the loctite set up before you install the stud and you use it on the aluminum threads sparingly before the helicoil is installed.
rt
Nope, doesn't work like that.
It is common when Helicoil wasn't done right.
The outer diameter of Helicoil is larger than the inner diameter.
The outer diameter is larger than the hole size it screws into.
Friction keeps it in place.
It isn't possible to prevent thread-lock migrating to inner part of insert and the bolt gets ;glued; to insert
I've hear a lot of supposedly 'experienced/trained' mechanics/techs saying to Loctite Helicoils in place, it's wrong.
If you want to use thread lock compound, use Timeserts, they are the bodgers friend as they hide shoddy work
