The block and firing pin both need to move freely, for different but inter-related reasons.
ETA: Sorry about the brief answer, I'll give a bit more detail now that I'm at a keyboard. You want to keep both the firing pin block and the firing pin/firing pin channel relatively free of oil. Oil will attract dirt and debris, which will adversely impact the proper function of these items. When the slide is closed and the firearm is ready to fire, the ejector is pressing up on the firing pin block. The firing pin block in this upward position is preventing the firing pin from traveling forward enough to poke out the end of the channel and strike the primer, sparking the load in the chamber. As you start to pull the trigger, the ejector moves forward just a bit, releasing the firing pin block, allowing it to be pressed downward by the spring behind it, freeing up the firing pin to move forward to strike the primer as the hammer hits it. If the movement of the firing pin block movement is restricted by a build up of debris, you could have one of two undesirable conditions: 1) the firing pin block is locked in the upward position, preventing the firing pin from traveling forward when needed, or; 2) the firing pin block could be frozen in the bottomed out position, allowing the firing pin to travel freely, and if the firearm is dropped, could potentially ignite the round in the chamber. The other component under discussion, the firing pin and firing pin channel, if clogged with debris, could inhibit the forward motion of the firing pin enough to cause a light primer strike, or, if clogged bad enough, prevent the movement of firing pin completely. None of these conditions would be desirable, and can be prevented by keeping oil from seeping into the channels in discussion. I hope this clarifies the concern we need to be aware of.