At UPS, each pilot has his own "travel bank." If you had a commercial DH leg that had an index of $1000 (this is the most UPS will pay for that ticket on that leg), and for some reason you didn't use the commercial ticket, you would get to "bank" 65% of that amount in your travel bank. In this case, $650 would go into your travel bank, which you could use at a later time.

Another example: let's say I'm ANC based, and my first leg on a trip is a commercial DH from ANC to HNL. The index for that commercial ticket is say...$1000. I live in San Diego, and would rather skip the commute to ANC, and fly direct from SAN to HNL. I can do this, but if the ticket on Hawaiian Airlines is $1300, I would have to make up the difference ($300) out of pocket. However, if my travel bank has $300 or more in it, they will automatically deduct that from my bank, instead of my paycheck. It's always nice to have some spare change in your travel bank.