When I did my GMO time with the Marines, we were directed to adhere to the current Tactical Combat Casualty Care guidelines (most of which are pretty reasonable). So my Corpsmen carried Hespan or Hextend, in addition to LR.
The two main arguments for using hetastarch were increased intravascular volume per pound of weight carried, and increased time in the intravascular space given the unpredictability and potential delays in evacuation times. As such, the justification for using hetastarch was always a logistic argument rather than a medical one, and even the logistic argument mostly fails these days. In Iraq, nobody walks and carries all their supplies in a pack - they're always within sprinting distance of a vehicle, which has extra supplies. Air evac times are typically under 45 minutes from first call to delivery at the OR, though this can be a lot longer in the mountains of Afghanistan.
I did hear of cases where heat stroke casualties were tanked up with Hespan instead of crystalloid, because the Corpsman in the field just thought Hespan was magical half-as-heavy-to-carry LR. I was less than enthusiastic about putting 1L of Hespan in every pack, not to mention the Combat Lifesavers' packs[1] but that was the order from up on high.
[1] A Marine with an extra week of first aid training
