When installing tile whether it be glass or ceramic or any other tile type you need to properly caulk certain areas with silicone to prevent moisture from wicking up behind your tile.
Where ever there is a change of plane within your installation is the area that needs to be caulked and especially prior to grouting.
Prior to installing your tile the seam between your backerboard and shower pan must be sealed and protected with a bead of silicone. If not moisture will wick up the backerboard or sheetrock and eventually cause damage. If you are applying transparent glass tile you will see this moisture behind your tile and the thinset adhesive will stain.
Before you grout you must also apply a bead of silicone to the corners where your wall turns, this is a change of plane and a red flag area as well.
Glass tile is non porous so you need not sorry about your tile absorbing moisture, the water has to go somewhere lets keep it where it belongs! Down the Drain Not behind your tile!