Flathead radiator with straight water

[Desoto291Hemi]

I know I am not that bright .
I read a lot of posts here where you should put straight water in the radiator with no antifreeze during a test .
Why ?

I have seen several pics here where the Block had a chunk the size of your fist pushed out ,,or a crack running the length of the pan rail or some other disastrous outcome from freezing .

I can understand doing for a short test,,,,,,but looks like too many are forgetting and leaving the water in without mixing in antifreeze .

What is wrong with putting some antifreeze in while doing a test .
If it is cracked already,,,,,the antifreeze won’t hurt any thing more than is already hurt ?

Just curious !

Tommy