According to the Eleventh Doctor, it was "outlawed in most galaxies" and something that could "disable whole vessels".
Ordinarily, the TARDIS was immune to magnetic hobble-fields because it had shield oscillators. However, the Doctor had put the TARDIS into basic mode, dropping those shields. Consequently, the magno-grab worked, and the TARDIS was brought into the company's ship.
The technology destroyed the TARDIS' engines and set the ship on an irrevocable path towards explosion which was only averted when the Doctor passed the magno-grab remote to an earlier version of himself through a time rift and thereby allowed himself to turn off the magno-grab beam when it was first emanated. Thus, the timeline in which the magno-grab trapped the TARDIS was wholly averted. (TV: Journey to the Centre of the TARDIS)