So I had a team of plasma fodd- new recruits go and take on a UFO. They all died but killed 4 of 8 aliens. When I sent the next batch in there were again 8 aliens.
This sort of discourages the player from accepting anything less than a total victory. I'd have been happy to send waves of less than stellar recruits in but I take a hit in relations for every attempt that results in less than victory and I can't do any permanent damage to the crash site.
Failure being a little less severe would encourage less save scumming and wider tactics. Also I have to wonder if this oversight could be abused... sending a strong raid team to weak crash sites and killing all but a couple, taking all the stuff you can, evacing and repeating to farm alien gear.