Best actor...Jake Gyllenhaal in Southpaw. Not even a split decision. He should have been nominated...at least.
Very helpful article! Generally speaking, cutting, rather than boosting frequencies is a cleaner way to add intelligibility to any sound, especially in a dense mix that includes music, dialogue and sound effects. Phase distortion can rear its ugly head when adding dBs to any frequency, although using a phase linear EQ will help.
Notching (narrow "Q") is usually used to eliminate feedback in a live sound setting, lessen the impact of environmental distractions, like a low frequency rumble, or correct issues arising out of incorrect mic selection or placement. Just a FYI...The wider the "Q" the more natural sounding the perceived change. Adjustable "Q" is used constantly in the mixing world.
This article also touches on a critical, general rule of mixing. Each sound in a complex mix should have an individual EQ "home". Consider this: A symphony is arranged in a very specific configuration to enhance the clarity of each instrument and especially how they interact with each other. For example, The violins are seated in the front, then woodwinds, then the brass...the kettle drum is in back. This creates a live mix that enables each instrument to be heard clearly. This works not only due to the relative volume of each instrument but also their timber/tone, or EQ "home".
By simply identifying an individual center frequency for each sound element, usually by slightly cutting overlapping frequencies of it, or other sounds adjacent to it, you can add much clarity and impact to a mix. When done correctly, each sound is no longer "fighting" for space in the mix. Always utilize this technique before you reach for a volume fader to increase ineligibility. There are many other mixing techniques that could be discussed, but this one is particularly foundational. Hope this helps! Love this site!