DoomIhlVaria
Cipher
AKA if you infuse a weapon that does 240 physical with a fire gem.. it will now do 120 / 120 split.. but because of how defense works in the game those two damage pools of 120 / 120 will overall inflict lower damage than a straight 240 physical. With some exceptions as I mentioned.
The exceptions are pretty interesting though. The Deep mod doesn't split your damage, it merely destroys strength and dex scaling. The base damage stays the same and then you get an equal amount of Dark damage. This is crazy powerful when your strength and dex are still low. You can get a pre-modded Deep Battle Axe very early on. The lack of strength scaling also means that you don't really lose any damage by one-handing rather than two-handing. Raw works in a similar fashion but I don't know the percentage it increases your base damage off the top of my head.