Q: Why would you want to increase the FPS if the animations were designed for 60 FPS? If the animation frames don't exist you can't render them.

A: Factorio animations are actually not tied strictly to 60 FPS. All three levels of belts for example have 32 animation frames, but Red and Blue belts generally only render every 2 or 3 animation frames to match their speed. Objects on the belts themselves don't use animations at all, and can be drawn in a new location every frame. Put some beacons around a factory or exoskeletons in your armor, and you are missing frames in those animations at 60 FPS as well. Inserters are not animated, but rather drawn procedurally with vectors. Weapons, particles, vehicles, and biters can all change their positions every update.

Most importantly however is the camera. While moving around on screen, the camera moves less distance more often which is a much more pleasant experience.

All of this assumes of course that you have a monitor that can actually display more than 60 Frames per Second.