[JLS]

"His rabid insistance on getting that first "scratch" Purple Heart tells me he was already planning on getting his "three and go home" Purple Hearts. Otherwise, why bother hassling commanding officers for that bogus first one?"
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Maybe because you never know if you are going to get "wounded" again or not. If your goal is to go home and run for office and you think having won a purple heart will help, you take the first one that comes your way and do not risk not getting one. So it might have been a three and home strategy or it might have been get one to enhance your political viability to steal a phrase from another Dim. And there may be more explannations that these two.

[Travis McGee]

Correct. And both explanations are not mutually exclusive, and both point toward using them in a run for office.