Q:

In what way was Murph's quantum data from her Dad's watch helpful?

How was humanity able to use the quantum data that Murph received from her dad's watch in Interstellar?

A:

It enabled Murph to complete Professor Brand's equation which was required to enact "Plan A" for the evacuation of Earth.
Brand and Murph had previously been unable to complete this equation as such quantum data was only available from a black hole. TARS going into a black hole and transmitting this data back to Cooper in the 4th dimension, who then tranmitted it to Earth via the watch, allowed for its completion.
EDIT: Updated answer above - it was actually TARS, not Cooper, who got the quantum data, as pointed out by ed0.

A:

Dr. Brand, had already solved the necessary equation, which was required for the 

question of how humans can escape Earth's gravitational pull en masse.

But he needed some more data from a singularity behind a black hole to complete it. All this was needed for safe migration of all humans from earth to the other planets, and this indeed was PLAN-A.
Cooper gets this data from TARS and translates it to Murph, who successfully completes the equation. (Murph is seen tossing the papers in joy.)
And yes, humanity able to use the received quantum data. While an exodus is not shown, it clearly evident from the last scene where a new human colony has been established, which is currently revolving Saturn (as stated by the doctor who attends a recovering Cooper.) Dr. Brand's daughter also succeeds in reaching another planet which can sustain life, but till the movie's end, she was the only one on that planet.

