New
#21
Using the card to force a bit of TIM into the imperfections is called tinting and is done more often than you may think, especially on coolers that have direct contact heat pipes. Those usually have a little crack between the pipe itself and the base the pipe is embedded in. Tinting fills in that crack (along with any other microscopic pits, etc.), eliminating any metal to air to metal interface.
One can avoid killing the CPU's warranty by lapping only the cooler. That is the surface that is usually the roughest (relatively speaking) and can usually benefit the most from lapping. Coolers are far less expensive than CPUs and voiding the warranty on the cooler will have much less of a financial impact if things should go pear shaped.
While most people will not benefit enough from all that, it could make the difference between a functional PC and a toaster in marginal cooling situations or when one thrashes the living snot out of the CPU.