Customer currently can't get their gift voucher until their order is manually processed at a till which can be an issue for shoppers that are in a rush.
Example:
If a customer is last minute gift shopping and buys a Gift Voucher Friday to give to someone on the Saturday, and they place their order after we close. They won't get the voucher until Monday (Tuesday if it was on a Bank Holiday) and those doing last min shops on Christmas Eve would not be able take advantage of this feature either.
Most sites I have used issue their voucher codes immediately, so providing the ability for Online Gift Vouchers to auto-process at the time of sale would be highly beneficial for the customer and everyone who uses voucher codes on their site.