domed vs flat

[JointTech]

i know for you old hats this has probably been beat to death. Im about to start the adventure of building my first engine and as I research I come up with domed and flat top pistons.
i understand the principle of a dome making the combustion chamber smaller thereby increasing the compression ratio.
what I dont understand is why you would use domed on a new build when you can choose the chamber size of your heads during the build.
is there some reason aside from raising the compression level which could be done in the head anyway?