David,
We tap our blocks because we use the HV/HP type of
oil pump and feel that it just makes good sense to be sure they can not get out. Of course you do this BEFORE you start building the engine.
One other thing to remember, even after you get your block back from the machine shop and it looks all clean and ready to put together IT IS NOT CLEAN! Always wash your bare block with solvents followed by HOT soapy water. Run a lint free rag up and down the bore until it comes out clean. Then clean the bore one more time to be sure your lint free rag really is lint free. Just remember to clean everything that goes in or on the engine.
You can tap the freeze plugs but we use brass plugs as we are in Florida and rust is more a problem than the cold hard freeze that makes plugs pop out. I have never seen a need to tap the freeze plugs but like everything else that is just my opinion. For what it is worth.