A guitar tone control does 3 useful things. But first it's important to understand that guitar circuitry adds a high frequency peak with treble roll-off above that peak frequency.
(1) At maximum (setting 10) it loads the pickups at high frequencies, so the high frequency peak has less "level". This is often desirable for bridge pickups, maybe less so for other pickups. In this situation the peak is mostly caused by resonance between the inductive pickup coils and cable capacitance. Although this can be simulated with EQ, it would be tricky to do it exactly the same unless you measured the resonant frequency and its Q, and always used the same cable.
(2) At settings below 10 down to typically about 3, it lowers both the level and the frequency of the peak, giving a useful range of less bright tones.
(3) At settings below about 3, the tone capacitor adds to cable capacitance and boosts resonance while lowering the resonant frequency even more. Setting 0 is useful for a sound effect similar to leaving a wah pedal in the heel-down position, and popular for typical muddy/resonant jazz tones.