It's still pretty useful to do simple math in your head. For example chicken adding a few numbers together or multiplying something. In general stuff that would take longer to type in than just calculating yourself.
If it's not important enough to take a few seconds to a minute typing it, it's not important enough to use a skill that's severely atrophied from decades of intentional disuse 🤷
That sounds like an incredible amount of work vs just adding rough estimates together. I can add two numbers in less time than it takes to reach into my pocket.