In short, mirror components help you:

• View the full context of a record in one place

• Reduce back-and-forth navigation between modules

• Reference live data from related modules without duplicating fields, consuming field limits, or affecting Reports, Workflows, or Automations.
  
  

Notes. 

1. The Mirror Component is always in sync with the parent field.
   
2. Any changes or modifications made to the source record will be reflected instantly, ensuring that users always see the most current information.
   

How to Use It  

From the dependent look up fields -

1. Go to Setup > Customization > Modules and Fields.

2. Select the required module.

3. Add a Lookup field and link it to the related module (eg. Accounts in the Deals module or Contacts in the Cases module).

4. Save the Lookup field.

Notes.

1. Unlike other fields, mirror components are exclusive to the create, edit, and the details page; they aren't visible in other views like the list view.
   
2. Mirror components can't be used in criteria and filters. However, if a user wants to use the related module fields in criteria and filters, they can use cross-module filters in custom views and smart filters.
   
3. Field limits: Zoho CRM supports up to 100 mirror fields per module, across a maximum of five lookup fields. For instance, one can add up to 100 mirror components for one lookup field or 20 mirror components for every five lookup fields.
   
4. Supported Field Types: Mirror components currently support the following field types:
   
   • Single Line
   • Multi-Line
   • Email
   • Phone
   • Pick List
   • Multi-Select
   • Date
   • Date/Time
   • Number
   • Auto-Number
   • Currency
   • Decimal
   • Percent
   • Long Integer
   • Checkbox
   • URL
   • Rollup Summary
   • Radio buttons
     
5. Layout-specific behavior: Mirror components are layout-specific.
   
6. Data Association: If lookup association is removed, the corresponding mirror field disappears. When a new record is selected in the lookup field, the mirror fields immediately update to reflect data from the newly linked record.
   
7. Access Permissions: 
   
1. Module Access - The user must have access to the lookup field.
   
2. Field Access - The user must have permissions to view the mirrored field in the parent module.
   
3. Record Access - The user must have access to the specific record linked via lookup.
   
4. If the lookup field is empty, the mirror still appears (but shows no data).
   
8. Deleting: The mirror field will be deleted when the lookup field, or field in the lookup module, or the lookup module is deleted or disabled.