When an employee submits a W-4 it contains information vital to them particularly their tax filing status and any additional withholdings they requested. For example if an employee is claiming married with 1 exemption and also withholds an additional $50 per pay period the pay stub would normally include this information on it in a form such as Fed WH: M-1/$50.
QB desktop included this information on the printed pay stub. But QB Online does not allow this to be printed. When an employee changes their W-4 there is no verification that the change was ever implemented because it does not appear on the pay stub any longer. This can have serious implications at tax time for the employee who assumes they've had the correct filing status all year only to find out they did not, and didn't know about it because it doesn't appear on the pay stub.