Normally, if you apply a vignette effect to a photo and then crop the photo you will crop off some of that vignette effect at the edges, too. However, Lightroom’s ‘post-crop’ vignette will re-apply the vignette settings after the image is cropped so that you don’t lose the effect. MacPhun’s Luminar has a Vignette filter which offers both modes – pre-crop and post-crop vignette.