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You may come to find that 'seems fine' and 'is fine' are two VERY different things, especially when you're talking about precision machined parts operating under significant force and thermal extremes.

A crack which is not visible to the eye can open up a disastrous amount once the head is torqued in place. As they may be difficult to see with the naked eye, florescent or UV reactive dyes are applied as they will be sucked up via capillary action and thus highlight any cracks under UV.

A warped head or block can have an excellent seal in most areas but one weak spot can blow in a week and ruin all of the efforts you've put in to it.

Pitting is a bit of both of the above in many ways. It acts like a crack as the coolant may be able to just push through under certain conditions due to the HG not having enough pressure in those areas much like warpage causes; If moisture manages to move through it on a regular basis the cavitation will continue to erode the block or head at an ever increasing pace.

If you ignored any significant pitting or didn't check anything for warpage well, it's a bummer, but anyone with shop experience and 90% of hobby mechanics would have told you right away that those are a must (it's covered in the manual too). The same goes for running a thread chase though all of the threaded headbolt holes in the block.