.LRV files are low-resolution video copies created by the GoPro. They’re mainly used for quick preview and playback, especially in GoPro mobile apps, because the smaller files are easier to stream and handle with less lag. They can also be useful for editing on a less powerful computer as proxy files; you can even rename an .LRV file to .mp4 to view it.

If you delete them, your original high-resolution video is still what matters for final quality, but some app features and smoother preview/playback may stop working or become less convenient. In short: they’re not your master footage, but they are useful support files.