This is about controlling the dynamics of the low end (particularly on palm mutes), it's quite different to filtering low end because that frequency range remains at roughly the same level. It's just about stopping that frequency range occasionally getting too loud on palm mutes. And its not something that Andy or anyone else does every mix, its just something anyone would commonly do to achieve the desired sonic result in certain circumstances If someone ALWAYS filters out their low end, or ALWAYS compresses their lows/low mids, then it's arguably more dumb than never doing any processing to the tone.
The worst mistake people make with dialling in sounds is adding processing without knowing why, or without any real aim. Going out looking for problems and fixing them just leads to sucking all the life out of a tone.