Certainly I will implement this suggestion as well but just wanted to know is this required even if my signal frequency is very low say less than 100Hz.

Yes, because the edges of signal are very fast and contain lots of harmonics!
Also, if you use an edge of such a signal at the recieving end of cable to trigger a flip flop or something else, then, when not routing ground return lines as close as possible to digital signal lines, problems can arise due to ringing and reflections. Mathematically spoken: A wild wire routing shows an unpredictable characteristic impedance, which is not at all suited to transmit digital signals with fast edges. A flat cable with many ground return lines next to digital signal lines, on the other hand, shows a characteristic impedance, which matches much better with typical source impedance of 74HCMOS gate output (about 50Ohm).

Kai