Increased fan speed will lead to lower temps, depending upon how effective it is and also on airflow within the case. I assume in a laptop this would help all components (esp CPU / GPU / mobo / HDD) as their exhaust will all leave from the same point. Lower temps can lead to longer product lifespan.

Increasing fan speed will lead to greater noise being emitted by the fan and can lead to a reduction in the life span of the fan. The battery will also be drained faster.