The system can handle the load if properly installed, but there seems always to be a bit of temperature overshoot at full throttle. You can set lower temperature as a constant and be comfortable, whereas with setbacks a higher temperature seems necessary to warm things back up. Naturally if you are away for a few days, then reducing the temperature make sense, but for only part of one day, the fuel burned to recover may equal the fuel saved at the lower temperature. Do a search here for setback, and you will have lots of opinions!--NBC
Steam systems are usually high mass, my boiler weighs close to 500 lbs and the radiators and piping several times that. It takes some significant energy to get all of that up to temperature.
My system goes down to 60 at night and up to 63 at 6am and then up to 66 at 4pm. I don't know if this is more efficient but I like a cool house at night and a warm bathroom in the morning; I used 435 therms of gas last year for heat. I'm usually sitting and reading as the sun goes down so i appreciate the extra warmth as it cools down outside.
Smith G8-3 with EZ Gas @76,700 BTU, Single pipe steam