Consider the following hypothetical scenario:
A large-scale terrorist strike happens in a major Indian city. Indian establishment decides to respond with brutal conventional force.
7 days after war declaration, IAF gains achieves considerable air superiority over Pakistani airspace and effectively disables PAF's nuclear capability. This happens while Indian Army's IBGs thrust deep into Pakistani territory, and capture strategically valuable landmass. Pakistan's National Command Authority decides to respond with nuclear strikes against the Indian stronghold over the captured area.
The air-arm is gone, so they resort to ASFC's missiles. Why won't they use Hatf-II/III? Because the Hatf-series has simply very big visual signature (big TELs, large number of support vehicles etc), is relatively inaccurate (CEP = 0.1% of range), and has higher yields (reduced yield warheads can be deployed, but that would be costly since expensive missiles are being used).
Here is where Nasr would step in. A small 6x6 TEL with upto two support/command vehicles can drive stealthily up close, launch 4x tactical nukes at the captured area in an even pattern and get out before the artillery responds.
This will provide both countries a chance to negotiate a ceasefire by themselves, if not then alarm the international community to enforce ceasefire immediately, and will effectively create a stalemate-type situation. If anything else, the ball would be in India's court, and what happens next would require a whole new pair of balls rather than a piece of paper stating the NFU.
India has the capability to develop tactical nukes, but hasn't produced and deployed them yet.
