When the Pi 2 was new, it was one of the few single board computers that properly supported fractional frame rates, which are often needed for smooth video playback. (Many films are encoded at 24000/1001 fps rather than exactly 24 fps, for example.) I assume the newer models still support this, since they're still built around VideoCore chips.

A faster model would allow decoding at higher resolutions and frame rates, even when the codec in use doesn't have direct hardware support.

With the PCIe support in this new model, it could also make a decent home file server.