What is the use of converting metre gauge to broad gauge trains?

Question

What is the use of converting metre gauge to broad gauge trains?

Answer 1

Increased capacity for tonnage, pure and simple.

The ability to move more tonnage per train equals more bang for the buck.  The broader the gage, the more the tonnage.  But, there is a point of diminishing returns.  Anything broader than 5' begins to become more problematic than advantageous.  That is why 5' gage is something of a rarity.

Answer 2

Probably for standardisation. If you have a system with two different gauges you have two networks, which can be expensive and complicated, so it makes more economic sense in the long run to convert everything to the same gauge.