There are lots of things in math that aren't really necessary anymore.  These date back to the days (daze) before calculators.  Lucky for us, we still get to do them!  Once something makes its way into a math text, it won't leave!  (Much like a fungus or a bad house guest.)

So, let's go back -- way back -- to the days before calculators -- way back -- to 1970!  There were no VCRs, no cell phones, no answering machines, dinosaurs ruled the earth!  I had to walk three miles to school in knee-deep snow...  uphill...  both ways!  It was awful!  (sniff)

Anyway, before calculators, math geeks had to crunch out decimals for things like

by hand using long division!  (Yuck.)

They had tables that listed decimal values for radicals: