Originally Posted by
TRAVELSIG
Specifically in the terms and conditions it explains that the value must be spent all at once and if the value of the ticket is less than the voucher there will not be any carryover (so, yes you are correct that leftovers are "lost").
The very best tickets to use this for in terms of simplicity are if you fly to one destination that costs more than 300 EUR on your regular fare and you can redeem it through the website swiss.com.
Thanks. The rules were not totally clear, as it mentions that it may not be spent on multiple pax. I guess that can be read as that it needs to be spent at once. Does the voucher also cover the YR/YQ and so on?