GOB LED display is by doing a layer of transparent glue on the surface of common LED display modules, and commonly indoor modules to make it have certain level or protection against water-splash, scratching, dust and so on.
With this layer of protection, the led lamps are more stablely fixed on the printed circuit board.
for indoor displays, where people can touch it, or installed somewhere there might be water-spash, this can be a good way.
Here is the comparasion of the SMD led display and the GOB LED display surface
SMD LED display module surface