It might be useful when most tiddlers are shorter than the screen height.
I think of this as being analogous to snap behaviour when using a grid in graphic vector software or CAD software - in some situations it is very useful to have snap to grid or nearest anchor but you have to be able to turn it off quickly and easily.
Any form of snapping is making decisions on your behalf to make life easier but it is also a reduction in choice and control - so to avoid frustration it is essential that the turn off mechanism is very quick, and easy to get to. Think of an image longer than screen height on mobile and your wish to scroll to a position where you can simultaneously see points A and B in the image.