One of the big reasons for this sort of thing is that people often don't understand how such systems work, so when it's too warm they put the temperature setting right down, which the system then works to meet, and then they find its too cold, so they put it right back up, and the system then works in the opposite direction.
The result of this is that the system ends up "cycling", using a tonne of energy and putting a heavy load on the hardware, all to produce a result which isn't comfortable anyway.
What would have made more sense, however, is if the system was able to compare against the outside temperature, so that it works to a range of maybe 17-21ºC, aiming for the low end when it's cold outside and the high end when it's warm.