On slow days, I don’t want to raise my efficiency that much , I take my time and review more thorougly. But on busy days, where I bill 13+ billable hours for a week, I’d want as much efficiency as possible.
I don't think you're really talking about "efficiency" here. On slow days, you may want to spend more time to do a more thorough job, but you still wouldn't want to be less efficient.
Simple automation example: renaming files into a new format. If there was a tool that could rename a large number of files for you quickly, you would use it on slow days and busy days. There is nothing to be gained to doing it manually.
I think you're referring to tools that speed you up but sacrifice quality. That isn't a pure efficiency tool, it's tool that allows you to adjust balance your time and quality of work.