Better explanation.

Timing the motor has another name too: static timing. Increasing static timing reduces bottom end acceleration but increases top end speed. The motor will run less efficiently and produce more heat.

Boost timing is different. It is applied only when the motor is going faster, and it can be ramped up slowly. The result is basically as if you had no static timing down low in the rev range (fast acceleration), and a lot of static timing high in the rev range (increased top speed). The best of both worlds basically.