What's all the hype and benefit about milling cylinder heads. I've always heard the first step in cylinder head upgrades is to have them milled .30 thousands. What's the benefit with this? Doesn't that essentially just reduce the combustion chamber volume? I know that increases compression, but is there another benefit to flow as well?

I didn't think so.

milling should not affect flow. what we normally would do is to make sure the surface is true and if not just have enough milled for a good head gasket surface

Pretty much done for 1 of the 2 reasons.

1st and formost is to true up the head surfaces like circle racer said.. Any high/low spots, rough places, etc that would cause a sealing prob.

Second is to lower chamber cc to gain compression.

.030" is a lot to take off in most cases. .006" to .007" = 1 cc so thats around 4 to 5 cc's removed from chamber size