It gives you more tonal control on the bass.
If you are only using a bass and an amp, and plan to EQ on the amp, then this is no big deal (though I find it much more convenient to do on the bass.)
If you only use light effects and preamps, this is no big deal (though still convenient to have on the bass).
If you plan to use a lot of effects, it is a big deal. At that point, the EQ on the bass controls the tone of the bass before effects. Preamps in your effects chain will EQ the wet, effected sound, including all the harmonics and so on added by some of the effects. And the amp EQ is then post everything, and useful for shaping sound to the room.
There’s a lot of reason to tweak EQ all the time, too. For example, slap (and sometimes pick as well) sound much better with some mid scoop at the instrument end of the chain.