Alright, hold on. That's a pretty broad statement. A good manual calc from someone who knows what they're doing is solid, but computers are really good at running through a million variables fast. The fight isn't manual versus computer, it's about knowing when to trust the printout and when your own experience spots something the program missed. My old boss used to say the computer estimate gives you the rule, and the manual check finds the exceptions, like that one weird circuit in an old house.
Yeah, the "manual vs computer" thing. It's not really a fight. They're just different tools. The computer runs the numbers for a standard setup. But your eyes catch the weird stuff the program doesn't know. Like finding knob and tube wiring hidden above a drop ceiling. The printout doesn't see that. You do.