what would happen if we use needle shaped nose in blended wing?
I assume you talk about the airfoil's nose, not the fuselage nose.

A pointed nose will cause flow separation in subsonic flow if the angle of attack is only slightly different from the angle of the leading edge. This flow separation will mightily increase drag because now no suction peak at the nose will develop. This suction peak is causing what is sometimes called "leading edge thrust" (PDF!). Without it, the aerodynamic forces will act in a direction orthogonal to the wing's surface and not (almost) orthogonal to the flow direction.

In pure supersonic flow the pointed leading edge is superior, because it causes less wave drag. However, it is preferable to sweep the wing such that the flow around the leading edge will stay subsonic even in supersonic flight, precisely because it still allows leading edge thrust to manifest itself.