As this block holds its sprite's Y position, it can be used when a script needs to know its sprite's Y position. There are many cases of this - for example, you could use the block to detect how far right you are on the screen.
Another use is setting values based on a movable slider - the script sets the value to the slider's X position.
Other common uses are:
- Changing a sprite's speed based on where it is on the screen
- Comparing the Y position with a record to check for movement
- Constantly storing a sprite's Y movement so it can be reenacted later