A calculator, for me, really doesn't replace the utility of being able to do some basic mathematics in my head. Even if you don't run into a lot of uses for mental math, I'm in the camp that thinks learning 1-10*1-10 and building a sense for numbers will aid in understanding of other concepts and in developing other cognitive abilities. Some carefully designed experiments could convince me otherwise.

It's not about having a calculator. It's about making quick connections when encountering new facts or numbers. Without sizeable core of memorized facts, results and numbers you will miss a lot of those. It's the very definition of being not that smart.

I often leave my phone at home to clear my mind and get away from things. I try to be phone free for about 4 hours a day. And during this time I almost always go out. And often I use my multiplication table during this time.

Being able to easily calculate e.g. $/100g to a rough degree without reaching for your pocket is super handy.

I think we could gain from emphasizing math with orders of magnitude, and knowing 1/n's would be super handy too.