Hi all,
The option for the Indexing amount is there to make starting a new year easier if you have a large number of employees.
If, for example the personal amounts are indexed (increased) by 5%, it will increase the total personal amount by the 'amount subject to indexing' times the rate. So if your personal amount is 10,500 ($1000 plus $9600 basic exemption), and $9600 is indexed, the new personal amount $9600 * 1.05 + $1000 = $11,080 is automatically changed based on the index rate when starting a new payroll year.
In the real world, peoples' situations change fairly often and we're under 50 employees, so I usually Email out new TD1s every year.