My employer's policy is to encourage the use of nonrefundable tickets, unless fully refundable tickets are only $200 more. My employer's policy is that, in the long run, the company will pay less, despite having to pay change fees and occasionally having to eat the entire cost of an unused ticket.
The legacy airlines' rules for business travelers are the same as for leisure travelers. The rule for nonrefundable tickets is typically that the value of the ticket, minus a change fee of $100 ($50 on some routes), can be applied to future travel for the same passenger (for a limited period of time), if the original ticket is cancelled in advance; but if the passenger fails to cancel and fails to show up for the flight, then the entire value is forfeited.
When buying airline tickets in advance, business travelers and leisure travelers can choose between expensive refundable tickets and inexpensive nonrefundable tickets. It's a good idea to understand the rules before making the purchase.