If you work in Lightroom quite a bit, I'm sure you've encountered a situation in which you wanted to compare two images or keep one open while working on another. Lightroom offers a few ways to do this, but using the Second Window function might be one of the more helpful ways to do it, particularly if you're working with multiple displays.
As this helpful tutorial from Anthony Morganti demonstrates, there are often times when you'll want to have a second image displayed while you either browse through a collection or work on a separate shot. And while Lightroom has several options for this, such as Compare view, you'll often want the primary image to still take up the majority of the display, with the secondary image just providing some sort of visual reference, such as keeping the original photo in view when choosing a sky to swap out. This is when the "Lock to Second Window" option comes in handy. When I'm traveling with my laptop, I keep a smaller USB-powered secondary monitor in my bag so I can keep chats open while my edits are full screen, and this is a perfect situation for such a trick. Give it a try!