Maybe it's because I'm a night person, or because I don't have much natural light in my room. But I just like my screens dim.
I couldn't find a good screen dimmer for my multi-monitor PC setup so I evolved on an existing one I found in the wild. Check out my fork of DimScreen for a multiple-monitor screen dimmer:
If compiling source code isn't your thing, you can grab the installers from Releases.
Note: requires .NET 4
I can see myself automating this very much like Flux, which only changes the colour temperature of the monitor.