Why did NASA intentionally crash the Lunar Atmosphere and Dust Environment Explorer (LADEE) on the moon?

LADEE was going to run out of fuel, and they wanted - and succeeded - to collect data of Moon's atmosphere and levitated dust.
(LADEE means 'Lunar Atmosphere and Dust Environment Explorer'.)

Fuel is needed to compensate orbital degradation due to Moon's non-symmetric gravitational field.

Online communication was possible due to superfast laser data transmission (Lunar Laser Communication Demonstration, or LLCD).

More details here and here.