When I was in high school, I got a new calculator - my first scientific calculator. It wasn't one of those fancy graphing calculators, nor was it programmable. But it did have lots of buttons and functions, and it was shiny. Excited by my new toy, I would use it for all sorts of things. I could evaluate complex equations in a flash! It was great! So, I started using it for everything, even for simple calculations that I used to "waste time" doing in my head. No more would I leave an answer in its boring 3π/2 form - I would evaluate it to 9 decimal places!
Before long, I was using the calculator to evaluate trivial things like 7-9, just "to be sure" it was really -2. And gradually, the calculating part of my brain started to atrophy. I relied on my calculator for everything, so my brain didn't need to think or calculate, just remember. I had no idea at the time, but my numeracy skills were slipping badly.
It took quite some time before I realised I was relying on this number-crunching "crutch" far too much, and I didn't like it one bit. So one day, I decided to leave my calculator at home. I forced myself to calculate everything in my head, doing long division where necessary, writing out the expansions of a large multiplication, and leaving answers as vulgar fractions.
It was slow at first, but eventually my calculation muscles got the workout they needed, and I became quite fast. It took some effort, but it was worth it. I still used my calculator occasionally, but I relied on my built-in one most of the time. Eventually my calculating muscles came back, and I was all the better for it.
Oh, and it's probably worth pointing out that an answer of 3π/2 is actually more accurate than evaluating a decimal approximation - even if you do have 9 decimal places!