Well, they existed not only to mix ingredients, but to remove ingredients, and also to make dose sizes available to patients that aren't commercially available in the distributed doses.
I'm holding firm that if a patient needs a 1.0 or a 6.5 or an 8.75, that the commercially available doses don't work for the patient and the patient is entitled to a compound. And Lilly's single-use vials don't obviate that, as patients under FDA and USP guidelines can't be required to single dose themselves with two injections (drawing from two single use vials to equal one dose) nor to waste over 50% of an unbreakable package (single dose vial) to get a single dose.