The Rates (Matter) is a new related list on the Matter record. This related list has been added to assist in being able to search for a rate table on the billing creation form.
Prior to this change if you chose 'Rate Table' on a billing form there used to be a huge difficulty to navigate a large unfilterable list --> previously in the rate table look-up window.
Using the Rates (Matter) related list to 'Apply Rate Groups' allows you to be able to filter your search better when billing and choosing rate table.
Once you set a Rate Group to the specific matter it will create a duplicate rate in your rate table with an association to that specific matter. Then when looking up Rate Tables on a billing for that same matter - the table will be able to sort (filter) them by the Matter if you choose no not check Show All Matter checkbox.
Using the Rates (Matter) related list to 'Apply Rate Groups' allows you to be able to filter your search better when billing and choosing rate table.

Rates (Matter) related list ~ "New Rate" button ~ Creating a New Rate for the Rates Table

This step saves a new Rate to your Rate table that is able to be already assigned to the matter and associated to either a rate a group, a timekeeper, or both.
Rate Name - Choose a name for your new Rate table rate
Rate - set amount of your new Rate table rate
Charged Per - set if charged by Hour or Item
Rate Type - set if Time or Expense
Rate Group - Lookup available rate group to associate your new Rate table rate to
Matter - Lookup matter to associate your new Rate table rate to
Timekeeper - Lookup a timekeeper (Staff/User/Employee/Contact) to associate to your new Rate table rate - (if desired)
Active - Set to Active to allow use
Default - if desired
Click Save to save
Click Save & New to create another new Rate table rate
Rates (Matter) related list ~ "Apply Rate Group" button ~ Choosing from existing Rates Table Rates

This step associate an existing Rate from your Rate table - allowing you to assigned to the matter.
(Using the Rates (Matter) related list to 'Apply Rate Groups' allows you to be able to filter your search better when creating a Billing and looking-up your rate tables)
1. This step allows you to choose an existing rate group
2. Shows you the available rate (from the Rate Table TAB) that are not already assigned to this matter
~ Check off AND modify** (if desired) the details of chosen Rates
~ Click Add to Save "Select Rates to add to Matter" changes
* Note "test1" in the 'Select Rates to Add to Matter' section is not associated to the matter itself - However you see that the Rate in the Existing Matter Rates section is also "test1" - this is because when it was chosen previously from the Rate table - it was duplicated and associated to the specific matter - "Divorce Case" - this can be seen on the Rate table TAB (shown in Screenshot Below)
** You can ALSO choose in the above step to rename the chosen Rate table rate when applying if you choose to make it more distinguishable from the default unassociated rate table rate.
3. Shows you the chosen rate(s) - from the Rate Table tab - that are already assigned to this matter
4. Click Done to apply
Red: Default "test1" Rate table rate - Unassociated to any matters
Green: Associated "test1" Rate table rate - Associated to "Divorce Case" matter
Once you have chosen Rates (Matter) rates then you can create a Billing with a Rate Type of Rate Table

Create a Billing (see: Create a Billing ~ From a Matter) or Create a Billing ~ From Billing TAB)
1. Choose Rate Table form the Rate Type drop down
2. Click Lookup to find desired Rate table
Default Lookup

Already filtered according to Rates (Matters related list settings)
Shows only:
~ those Rates from the Rate Table that correspond to the matter related to the billing you are attempting to create/edit
~ those Rates from the Rate Table that correspond to the Timekeeper chosen on the billing you are attempting to create/edit
Choose the desired rate here if you wish OR proceed to next step
Check 'Show All Matters'

Shows:
~ those Rates from the Rate Table that correspond to the all Matter
Choose the desired rate here if you wish OR proceed to next step
Check 'Show All Timekeepers'

Shows:
~ those Rates from the Rate Table that correspond to the Timekeeper chosen on the billing
Choose the desired rate here if you wish or proceed to next step
Check Both

Show all rates entered in the Rate Table
Choose the desired rate here if you wish or proceed to next step
Returns you to billing creation page

Shows Rate table rate you have chosen in lookup.