Even without a mech it is helpful. If you know you like a 0.5 ohm coil at 25 watts on your device it is really nice to be able to know I need x wraps at y diameter to get 0.5 ohms.Well, I will not be using a mech, but I do know about Steam Engine.
When I started these calculators were not really around. I could calculate ohms law to figure out safety for my REO but actually getting the right ohms in the coils was more trial and error making coil after coil until I figured out 7 wraps on this screw gives me what I need.