Even here on Earth it limits the clock rate and size of computers. Slow, slow, slow.
By comparison, if that same signal has to travel the entire circumference of the globe -- about 25,000 miles -- it takes a little over a tenth of a second.
The average human reaction time to perceive an event and respond to it is somewhere in the range of .5 to .75 seconds.
So a light impulse can travel around the world at least 5 times before we even know it left.
Say what you will, for human purposes on this planet, the speed of light is plenty fast.