Page 234 - Photoshop for Lightroom Users – Scott Kelby 2nd Edition

Step Six:
When all that’s left of the reflection is near the edges of the frame, head back up to the Brush Picker in the Options Bar and choose a hard, round brush, and
then paint right along the edges of the frame, and of course, try not to accidentally erase any of it (duh). If you do make a mistake, no biggie—just press X
to switch your Foreground color to black and paint the frame back in. That’s why we use layer masks instead of just using the Eraser tool, because if we
make a mistake, we can just switch to black and paint away our mistake. Nothing we did is permanent—we can always throw away our layer mask (just
drag it on top of the Trash icon at the bottom of the Layers panel) and start over. In short, layer masks rock (and I’m pretty sure Elvis did a song once about
them called “Layer Mask Rock”).