Nik Software’s Silver Efex Pro 2 is a really useful plugin that I’ve used for a lot of my black and white prints in the last few years.
Sometimes though, getting one part of an image to look the way you want creates unwanted effects in other areas. This is most noticeable in fairly flat skies, where darker objects (trees, buildings) poke up into the sky and have a slightly luminous halo round them.
As someone who mostly dislikes such artefact in their work, I noted that there is no reason for you not to apply the Silver Efex plugin multiple times to a colour image and blend the various black and white results.
A typical image that could show very visible halos if you were not careful