Typically Employer will need to set up Deduction Rate if there are rules stated that Employee will be penalized in the monetary form if they violate any of those rules, for example, late to work, absent from work, et cetera.
Setting up Deduction Rate is similar with Setting Up Overtime, except that some of the keywords might be different.
So, if you need guidance in setting up Deduction Rate, you can refer to the guide of Setting Up Overtime Policy.