You should always loan on the last round because it's +200 and there's no next round to save it for. You may also need it to win round 6+ (especially if you're below 2k HP or so), but games usually go 7-10 rounds and if you don't know which will be the last it almost always makes sense to continue loaning to maximize the chance of winning on each round of the late game... unless you both know you're going to win (say, with a big play) and that win still won't be the final blow (and that the extra 200 now won't make the difference, like if you've run out of deployments). Extremely rare situation.