In most cases, you want to use EQ on an individual track, to get it to sound right or to solve specific problems. But sometimes, your best bet is to strap an EQ across a bus so that the same EQ processes multiple tracks at once. For example, if you want a number of tracks to all share a similar tonal quality, for example if you want to add some midrange to all your guitar tracks, or a bit of “air” to all your background vocals, you’d be better off EQing the entire guitar or background vocal bus than to instantiate the same EQ on every individual channel. Also, if you have group of instruments that needs a bit of extra clarity, or perhaps an extra push from a frequency bump, an EQ across a bus is the way to go.
So if you find yourself wanting to shape the tone of multiple tracks that you are sending to the same bus, consider a putting an EQ on that bus, rather than on each track.