This is a great feature that we used to have on other wave editors back in the 90s.

When you're selecting a waveform and you drag the mouse below the view (the pink line in the screenshot) the selection of the waveform goes till the end.
On the contrary, if you're selecting and you move the mouse above the viewport, the selection goes to the beginning.

The selection is then performed on mouse up if the cursor stays outside.

This interaction speeds up a lot of operations that involve selecting the beginning or the end without the need of zooming.

NOTE: this is the same behavior of text selection on a single line text input when pressing SHIFT and Arrow key Up and Down.