The score and the time can dictate changes in tactics. If you are losing a close game, but have the artifact, it might be a good idea to have your carrier go ahead and devote full effort to fighting. This is the equivalent to "pulling the goalie" in hockey. Kills by the artifact carrier are worth more points, and those points could be enough to pull ahead in the last minute of a scenario, or it might get you to 500 just before the other team.
If you are losing and do not have the artifact, you might as well forget the carrier in the last minute or so of the scenario and just try to get a few kills. Earning a little more experience and renown is a good thing.