Sometimes it's to handle higher currents, other times it's to reduce the bond wire inductance and improve the high-frequency response. For power pins it can be both. Especially for a multi-chip module with some digital circuitry, there's potential for high-frequency digital transients that need nearby decoupling capacitors through low-inductance loops, or the transistor switching noise can pollute other copackaged circuit supplies; amplifiers also benefit from lower inductance on the supply lines since it stabilizes the frequency response at higher offsets beyond the loop bandwidth of any integrated supply regulation, current sources, bandgap references etc. So you're essentially correct, it's about voltage gradients, but probably at higher frequency.