If your gun is wireless OFF then it will be invisible on he matrix and will be immune to hacks.
In this case there is no need to slave it....

You also don't get the wireless bonuses.
If your wireless OFF gun is a smartgun and is connected to your smartlink with a wire then you can see the camera live feed to shoot around corners and you can see all the the information that game mechanic wise grant you +2 accuracy. If you don't wear your smartgoggles with your smartlink in (or because your smartlink is in the camera on your wireless OFF weapon) then you probably don't get to fire around corners and you probably don't get +2 accuracy either.
If your gun is wireless ON then it can be hacked from the matrix.
In this case your gun will get higher attributes when defending if you slave it to a master device that have higher attributes.
If your gun is wireless ON and you have DNI then you eject and change firing mode as free actions (doesn't have to be a smartgun or smartlink for this....)
If your wireless gun is a smartgun, is wireless connected to your smartlink you have DNI then you also get to shoot around corners by using the live feed on the on-board camera, get all the information that grant you +2 accuracy, a positive dice pool modifier, compensate for wind and both take aim bonuses. In this case your brain is connected to the wireless enabled gun and the wireless enabled link by DNI so you probably don't need to actually wear your smartgoggles and the smartlink can probably actually be located in your camera on the weapon.