The first computers took up entire rooms and they could only do about as much as a calculator. There was a point in time that having a computer do multiplication and long division for you saved you hours of time because the alternative was have 2 or 3 people do it by hand and then compare to check for mistakes.
Some of the code cracking computers used for breaking war-time ciphers were state of the art, and their only job was to check as many combinations as possible, way faster than any human could. Which left the actual scientists to find optimizations and analyze any results.