The Expand Selection command in the Block menu is only useful when selections are persistent. Persistent selections allow you to move the text cursor away from the end of the selection. The Expand Selection command creates a new selection that includes the old selection, and all text between the old selection and the position of the text cursor. The position of the text cursor becomes the new ending point of the selection.
The most significant difference between Block|End Selection and Block|Expand Selection is that End Selection pivots the selection if you’ve moved the text cursor above the spot where you started making the selection while you ended the selection below the starting position, or vice versa. This causes the old selection to be completely deselected, as the starting position stays put. Only the text between the old starting position and the new ending position is selected.
Expand Selection, on the other hand, always expands the selection. If the new ending is above the old beginning while the old ending was below it, or vice versa, Expand Selection simply makes the old ending position the new beginning position.
Whether selections are persistent or not, you can achieve the same effect by pressing Shift on the keyboard while clicking with the mouse at the position where the new selection should end. The advantage of Block|Expand Selection is that you can assign a keyboard shortcut to it and expand the selection with the keyboard.
Block|Between Matching Brackets
Block|Go to Beginning
Block|Go to End