Steve,
One of the reasons for using the TTOC() is the following. VFP stores DateTime data to the millisecond in the DBF but we only have access to the second. If we were to SEEK a DateTime value of say {^2001-01-01 12:00:00} we may fail to get a hit even if there is a record that "appears" to have that value. Why? Because our value has milliseconds of 0 while the field may have milliseconds of 1 thus NO HIT.
If the purpose of your index is simply to arrange records in an order, or if you only do searching in the index based on a range then this reason is meaningless to you.