In the mixing example, removing the bass from the side channels didn't improve the mix because the kick drum was intentionally placed in the side channels to create a specific stereo effect. The speaker found that removing this bass would negatively impact the song's arrangement, and instead chose to address other issues in the mix using targeted mid-side EQ adjustments.
This video explains how to use mid-side EQ to enhance audio productions, mixes, or masters. The speaker demonstrates how splitting a stereo waveform into mid and side channels allows for targeted EQ adjustments, improving stereo balance and overall sound quality.