Common clock signal to several components over long PCB lines
At 3 MHz rise times should be easy to maintain with the distances involved. In my experience most digital lines need a driver if the fanout is more than 5 or 6, and definitely more than 10. 

To determine fanout, one needs to know the source current of the driver pin and the sink currents of the receiving pins. The capacitance of the sinks also needs to be considered. One also needs to know what the voltage levels are of source and sink.