What is relevance of Norton's theorem over Thevenin's theorem
Both theorums side by side (courtesy of hyperphysics): -



Basically, Norton converts a bunch of resistors attached to a voltage source into a current source in parallel with a single equivalent resistor and Thevenin does the same except it converts to a voltage source in series with a single equivalent resistor.

The last time I used this was yesterday and I used both and I regularly use both.


  Are there any practical uses or importance of the Norton's theorem in
  any domain of electrical engineering


Yes there are. I had a voltage source feeding a parallel capacitor via a resistor. I converted the V and R to a current source. Now I have a current source with parallel R and C. I then converted back to a voltage source so it became R||C in series with the new voltage source and it made the problem mathematically easier for me.

In other words I broke down the problem into simpler jumps; I could have just done the whole math but there were other complications because following the R||C was another series capacitor and inductor to ground. (Basically it was solving the resonant frequency for a Colpitts common collector BJT oscillator and analysing the loop gain at resonance.

So I used Nortons, followed by Thevenins. I'd say I use neither quite often but when I do use one of them it's likely to be in equal amounts to the other one.

I'm aware that this answer is an opinion but I felt that giving an example was useful.