How is that the “easy things” are done by humans, often in paper and the “hairy” problems are done using a computer? Why not let the computer do all simplificat

How is that the “easy things” are done by humans, often in paper and the “hairy” problems are done using a computer? Why not let the computer do all simplifications and precalculations and precomputations? I am an external and maybe I see the things a bit different but if I should write a decimal number I would prefer to keep sqrt(2) as in my code rather than writing an approximate, almost equivalent, float. And I see formula simplifications and analysis in the same way... work to feed the compiler.