Valve lapping is crucial in a tuned engine, it is paramount in making the most out of that carefully crafted power stroke, you do not want escaping power!! In the old days it used to take hours "palm shuffling" but these days we have tools such as the "Oscillating Valve Lapping Tool" pictured above. It simple attaches to the chuck on your drill & oscillates the valve, its so effective there is no need to use course paste, just go straight to fine paste it only takes 5-8 seconds a valve!!!!!!
Titanium valves are coated the typical grinding paste used removes this coating so its important to understand that valve lapping cleans the seat only the above picture is of spare valves i use for this. The use of seat cutting should only be done when new guides have been fitted and or a different valve seat angle is to be used. The negative is every time you cut the seats your taking away materiel which reduces the shim gap & increases chamber space (decreasing compression)