The “Per Second” option is really only relevant when you have set the Operation in anything other than “Set”, so like for example “Add”, or “Subtract”.
If “Per Second” option is enabled, then ValueB is multiplied by Time.deltaTime, before “Added”, “Subtracted” or otherwise to ValueA.
You essentially can enabled “Per Second” if you for example want to increase (Add to) ValueA, by ValueB per second, while without “Per Second” enabled, the operation will take place per frame.
