Vignettes are a Nice Technique in Flower Photography. Here's and example
A great use for a vignette is with flower photography. It is a very effective way to focus attention on the flower(s) and to keep the viewer's eyes from migrating to the background, especially if the background is busy, in focus, and/or brightly exposed.
Applying a vignette is part of my workflow for flowers. I will usually use the radial tool in Lightroom to darken the area around the flower, all the way to the edges and corners. I will also back off on the sliders for sharpness, texture, and noise control, in an effort to soften the background.
If the vignette bleeds over onto the flower (it usually does), I will use the brush tool and the "erase" mode for the brush to erase the vignette effect from the outer edges of the flower, where the bleeding takes place. This allows me to bring the vignette right up to the flower without actually affecting the flower itself.
As a final touch, I incorporated the brush tool again. This time I set it at something like -.5 on the exposure slider to provide darkening by one-half stop wherever I applied the brush. I used this to brush over the lighter areas in the background so they are not distracting, but I didn't darken them fully as I wanted the flower to be viewed in the context of its environment. In this case it meant darkening the brightest green areas.
The image above is an example from yesterday. This is the final version, after processing in Photoshop and Lightroom Classic. It's a hydrangea that has begun turning pink. This is not a technically good picture. It is not worth keeping, except for illustration purposes. I used focus stacking to combine 10 images. But there was some breeze, which moved the flower a bit in each subsequent frame. This created a nightmare for photoshop to align the images. If you look closely you will see some ghosting of edges (no you do not have double vision) where photoshop couldn't align the edges of some of the petals. Aside from that, to get to this final image I used the workflow suggestions outlined above.
Some of the processing steps
The original image
There's plenty of room to crop to taste
I find the leaves distracting. YMMV
Vignette applied to darken and soften the areas outside of the flower
Final cropping. Tighter and with a 5:4 aspect ratio.
Applied a brush to the brighter green areas to darken and further soften those areas.
Same as the image above this one, except that Content Aware in
Photoshop was used to eliminate a couple of blown out (white, no detail) areas.