This forum is full of topics about saturation (tape, tube... how to use it... blah blah blah) and it seems that it is phenomenon of these days. I'm not professional music producer - just hobbyist - so I don't need spend hundreds dollars for VST every year.
TLs Saturated Driver is nice plugin for adding saturation (for vocals and synths) or distortion (for guitar)... I never used it on master channel. GUI is clean and simple, knobs are self explanation. There are also some presets to start with (not much, just 9 + 1 default), but I thing that's enough. In zip file you can find "readme.txt", but I think, that you will never need it. CPU usage is ultra low (2% in my old notebook - 1.6GHz). I use it mainly on lead vocals to add some presence and saturation, distortion (call you as you want).
You can also find some other "saturation-based" plugins on TbT website site (e.g. GreaseTube, TubeLimit...) but I consider this one the best of them.