Don't look at the trade as "saving" the current trade or "extracting a bit more" from it. If you've lost 10% on Trade A and you can make back half of that (maybe) by rolling, why would you do that if your average expected return of a new trade is 10%?
It's HARD to let go of losers, particularly when there's a chance they could turn if you make an adjustment. But look at each trade you do as a new trade and make sure it fits the same parameters as initially. In other words, if you wouldn't do that trade as a stand alone trade, you probably shouldn't be rolling. If you would do it, then by all means, go forward.
by @cwelsh