Group on Invoices Checkbox on Custom Transaction Column Field

To use the Group on Invoices check box settings, Invoicing Preferences need to be setup first:
Setup > Accounting > Invoicing Preferences

You can use the following options (for more information, review SuiteAnswers article (9189): Global Invoicing Preferences):

• Combine Time Items on Invoices
• Combine Billable Items on Invoices
• Combine Expense Items on Invoices

Important: If any of the options listed above is turned on, the Group on Invoices functionality is driven by the settings of the Invoicing Preferences.
All of the above listed items will be grouped on an invoice by the custom field with Group on Invoices checkbox turned on.
Grouping takes into account the different values in the line items' columns; if some of the values is different from the other values in the grouped lines, this line is printed as separate line.

Example: