What is the point of the Higgs Rig?

It’s a rig designed mostly for mining ships. Slowing down your maximum velocity allows you to spend more time in range of asteroids while moving at 3/4 of max speed and ready to enter warp.

The mass increase also makes it useful to collapse wormholes.

Finally, having +100% mass but -55% inertia modifier overall reduces the time it takes you to go from 0 to 3/4 max velocity, if you are trying to accelerate into warp to escape hostiles.