We're in danger of promoting bad practice again. Much of the stuff being talked about is 100% solid - BUT - only in context, and although you may well
see people do it - as in...
I've watched the pros do it while they are mastering music
Do you actually know what it was they
heard?
When you've trained your ears for a long time, you hear characteristic problems that prevent you doing your job. You then select an appropriate tool, and use it. Subtractive mixing is a perfectly valid solution to some problem mixes. Equally, adding a few dB at a specific frequency is another. Your real problem without experience and a trained ear is which one to use. The reality is that subtractive AND additive eq can be identical. With modern eq, adding 10db at 3.5K can be exactly the same as removing 10dB below and above 3.5K - the only real difference in practical terms is where the channel fader ends up!
The visual audio spectrum reveals any empty spaces, or over excited areas that your ear detected as 'something' wrong. As I get older and grumpier I'm getting quite concerned people are making music visually, ignoring their ears, following some kind of exotic recipe that promises audio excellence. Some music is wonderful because it has empty space in the frequency spectrum - people praising the clarity and openness. Other music is powerful because every bit of energy has it's own place, blending into a wall of sound, totally unlike Phil Spector's.
Take a side step into PA. Newcomers to live sound getting concerned about how much electricity supply they need for their 10,000Watt PA system. Doing the maths and demanding a power supply the venue simply cannot provide. The old hands then tell them their 10KW PA will happily run from a power outlet capable of just 3000W - because their music is full of gaps - in both frequency and time.
I know people who tickle the EQ controls, I know others that grab handfuls at a time - eventually, they meet in the middle.
The benefits of subtractive eq are usually removing unwanted or ineffective portions of each instruments output so it doesn't weaken something else's. If I want a dull 60s kick sound - I dump all the HF components above maybe 120Hz or so - which also removes spill. You could knock off the bottom end of the snare - making these two more separate - more control in the mix. Do you need the bottom from your overheads? What are they used for? The metalwork? - if that's all, a bit of sizzle, then again, chuck away their bottom - but maybe you also want a bit of mid range from the toms? Chuck away the very bottom? Leave the rest? Or maybe remove the very bottom and boost the 5K upwards? I can't write down the solution because I have not heard the drum kit.
Forums are great sources of information - but like recipe books in cooking - you must adjust for personal taste and the ingredients you actually have.
I have a tenor sax I play from time to time. I love how it plays. It sounds simply horrible. The eq I end up with when recording it matches nothing I have ever seen used by other people - odd sucks and boosts - just to get the damn thing neutral. That's not in any guide or book.
Too many people are making music by blindly following TAB, eking by internet consensus and treating rooms without even listening to them.
I hate visiting PA people who routinely blast out pink noise, and complain about the nasty peaks and troughs of the venue and spend an hour removing them, only to find the PA sounds simply dreadful. The reality is often that just because you can see something it doesn't have to be sorted - unless you can hear it!
I your mixes sound bad, they are. Go back and do it again, building it up logically based on what the music is. Got two guitars? EQ isn;t going to separate them but a bit of panning will, then perhaps you can change their overall tone gently which your brain accepts as they're not panned dead centre. Your brain hears them in a different location and the different tone splits them. If your drums are a mess, then gentle eq and panning can help no end there too. If the vocal is the most important feature in a song, then maybe that 2nd keys part should simply go or drastically go down in level to make space - NOT give it a weird eq cutting out the vocal range.
God I hate mixing by prescription!