If you're reading up about it, you're starting out right!
Heat sinks today for the most, are manufactured to a lot better finish tolerance than what was available in the earlier overclocking days, in those days lapping a heat sink was almost a must, the bases mostly looked like it had been cut with a circulating saw.
So to get any descent contact you almost had to lap the contact surface, or use a lot of TIM to fill the gaps, once overclockers got more demanding as to the end quality, it forced heat sink manufacturers to get competitive on their contact finish end results so things got much better for us.
So really today lapping falls into the extreme category, especially when it comes to heat spreader lapping, requiring almost zero TIM between the two mirror finished surfaces and usually a 2C to 3C cooler gain on the CPU side itself.
With my Q9550 setup, the heat sink base was on the rough side so lapping it produced a 5C lowering of the temp, lapping the heat spreader yielded another 3c and adding a second 120mm cooling fan gave another 2c drop for a total of 10C drop overall air cooling.
That put me in a range temperature wise of reaching a 4G stable overclock on the Q9550, now in that case, lapping was worth it, and in my opinion lapping is always worth it, unless you forfeit a warranty to do it.