If you tap and hold that, then you get a repeating effect: First one character at the time will be deleted, and then, after a few characters have been deleted, whole words will be deleted.
Dragging to the right (or up or down) on the backspace button deletes the character to the right of the cursor, one character at the time.
If you drag and hold, then you get a repeating effect. First one character at the time will be deleted, and then, after a few characters have been deleted, whole words will be deleted.
To quickly select all characters, draw a circle, starting on the 123/abc button.
You can also Drag and return either left or right to delete backward (i.e., behind the cursor) one word at a time.
Similarly, if you Drag and return either up or down starting from the back-space key, you'll delete forward (i.e., in front of the cursor) one word at a time.