GP means inefficient in the sense of cost. Paper ballots add costs. Partial manual audits / hand-counts add costs. Full audits / hand-counts add a lot of cost, and in particular hand-counts require a lot of staff in order to yield results on election night.

The costliest item is counting by hand, so... don't. Use ballot scanning and counting machines and then implement a timely partial manual audit to demonstrate that the BMDs and BSCDs functioned correctly.