One cannot think of a mathematical step without 'is equal to'. It balances right hand side and left hand side. It aids simplification and manipulation of a mathematical expression.
example:
2(A+B) = C
2A+2B = C
2A = C-2B
A = C-2B/2
In an electronic calculator, the pressing of ' = " sign executes an asthmatic expression or simply calculates.
In computer languages, it plays very important role.
A = B
When a computer looks at this expression, the value stored in the location named B is just transferred to the storage named A. After execution both A and B will have the same value and be equal.
Now consider this.
1.A = 5
2.A = A+1
3.PRINT A
Here in the first step, the value 5 is stored in memory A. In the execution of second line, 1 is added to the already stored value in A and now the A will contain 6. In the third line, 6 will be printed. This is how the computer languages like java, python works.
Next:
If S = 100% then display "download successful" else "failed". In this kind of logic statement, value in S and 100% is compared and the appropriate action is taken.
Hence "=" is a powerful symbol in many fields.