Honestly, when i got my second garret... i used one of them to AW my Bernice. Events just had such long breaks. Silvers got rare. What can i say? I dont intend to ever use garret but since im a collector i keep at least one copy of every rare unit. When i get a second one being as "useless" as garret though (heck even leannee makes a better second HA to bernice then garret) i can just as well save me some gold, save me some farming and save me 2 silvers.
Same would go for lets say Stray and AWing Archers like Bashira and Spica. Or your second cyrus when u already have mehlis and garania. The RC are not worth it as i dont spend so much that i will hit 1000 RCs anytime soon.
In my eyes using golds as AW fodder is absolutly acceptable if you know for sure u never itend to use them ever. (and if your like me u will keep around at least one copy anyways)