The first few seconds after the hook up are possibly the most critical moments of the battle. Marlin will often shake their heads vigorously the moment they feel the sting of the hooks.
The slack line created after the line releases from the outrigger is often all that a marlin needs to feed itself.
Tag lines are lengths of cord that cut out the drop back, reducing the chances of a fish throwing the hooks.
However tom complicate matters many anglers are now fishing light drags and no tags lines allowing the fish to turn and swimming away before upping the drag. Two different lines of thought experiment and see what suits you.