what is the benifit of not creating instance of a static class in c#?

in normal class we need to create an instance of the class but in static class there is no need to create an instance of the class.

so my question is

what is the benifit of not creating instance of a static class over normal class in c#?

The main benefit is that you save on memory. For example to get the maths constant 'pi', which is 3.1415.... it'd be a terrible waste to have to create an entire class every time.

var x = Math.Pi;

versus

var constants = new MathsConstants ();
var x = constants.Pi;

The first case is a simple memory read of a constant value. The second case involves allocating memory, running a constructor and calling a property. This is considerably slower than the former if you want to do it a billion times a second.