Laser Spot Tracker and LGB operation

Does the laser spot tracker (LST) in the AV-8B Harrier II’s nose have anything to do with LGB operation? Exactly what does the LST do?

AFAIK the USMC A-4M Skyhawks had a LST as well, but they didn’t carried LGBs. Neither do the AV-8B Harrier IIs with the same LST.

It seems the USMC Harriers almost always carry a Litening II laser designator pod when they fly LGB missions.

Cheers,
Sunho