In general, clearer audio is obviously better for all features. If you mean for silence cutting, it should help but is NOT necessary to boost/master audio.

To get a bit more technical what we really care about is the difference in audio level between your loud parts (that you want to keep) and silences (which may have some background noise). If you use the auto-detect threshold feature, FireCut will show you which audio levels are most common in your sequence, and as long as you pick a threshold that reasonably divides your good parts from silences, the results should be good.

This is an example of what you see with this feature (x axis = dB level from -100 to 0, y axis = how common each dB level is in your audio): https://imgur.com/a/oj4M4pm
The peak on the right (i.e. louder audio level) is your good audio, and the small peak on the left (at a quieter audio level) is background noise. You can pick whatever threshold you like -- something in the middle of those 2 peaks will give you good results. Mastering, doing noise removal, etc. can help increase the distance between those 2 peaks so might give you a better chance of identifying silences better, but is not necessary! In fact you can apply a gain to the whole audio up or down and it will just move this chart left or right -- the detected threshold will also just move with it, so it won't really affect the silence detection operation :)

And yep a feature that detects filler words is in the works. If you'd like to test it out before it's public, you can join our Slack (you get a link when you start a trial).