Industrial TNT is primarily used for more controlled explosions and collection of destroyed materials in processes like Mining.
Splitting up the charges and adding some nice cutting material results in the explosion caused by ITNT to be much more useful: It has less direct power, which means more blast control. Industrial TNT appears to destroy 10% - 15% of the blocks broken, where vanilla TNT destroys 70% of the blocks broken.
Industrial TNT also has its downsides:
if you left click it, instead of dropping as an item its fuse lights. While the explosion probably won't kill you it might destroy your buildings, farms, cattle, etc.
its fuse is slightly shorter
its blast radius is smaller than that of normal TNT; as volume scales with radius^3 the difference in amount of blocks excavated is significant.
You can not use Industrial TNT to make TNT cannons.