My GEQ is used to fill a hole in the mid bass (100-300 Hz) in my room at my listening position. I can flip the EQ in and out with a push of a button. I can clearly hear the increase in the "weight" of the voice and of instruments. In fact, I'm biased toward a mid-bass emphasis. That's another function of the EQ in my system. It helps me tailor the sound to my tastes. If my taste drove me to emphasize higher frequencies, I could do that with my EQ.
I'm not touting a GEQ as a must have. GEQ use can cause problems. Although the noise and distortion are far below any hearing threshold during normal use, if the gain of a particular filter is pushed too high, distortion at that frequency will happen. I have seen and measured this using REW. I have to be careful. There may be other phase shifts, etc...happening. However, I cannot perceive any audible effects from these.
I have measured with and without the GEQ. The data I have shows differences, but not any that I can point toward creating audible differences, except for the altered frequency response.
That's how I use the GEQ in my system. There are other means to do what I want to do. Traps of course exist. I have plenty of those. DSP. I tried very hard with this one. I found it no better than the GEQ and far less intuitive. And way more cumbersome.
Enough babble.
I really don't understand your final question. What should I look for?

