There are three basic kinds of EQ: Low/High cut a.k.a. High/Low pass, Low/High shelving (your basic bass and treble controls) and parametric (adjustable center frequency and bandwidth).

For equalizing program material, the application we're talking about there, if I had to choose just one, it would be the shelving filters.

You typically don't use narrow parametric filtering on program material for system equalization. If you find yourself needing to, you're likely dealing with acoustical effects. You can do surgical EQ and make things sound better at one listening position and make things worse at another. Better to attack the underlying acoustical issues if possible.

You do quite frequently use the narrower filters on individual tracks in a production to remove unpleasant resonances or punch something up in a mix. And we do use them in live sound reinforcement for the same reasons and for feedback suppression.