Reasons for partial tiles in Sentinel

The tiling system is an artificial system used for dissemination of files that has little to do with the actual satellite images acquired. As such, if the image acquired only partially covers a given tile, you will see NoData in the image.

To give an example of this, I've made this illustration. The imagery is the full Sentinel-2 acquisition in the area, while I've added a rough outline of tile 32TPL in red. As can be seen, the acquired satellite imagery doesn't align at all with the tile system and is in fact much wider than a tile.