Just sharing my experience so I'm not sure how "good" or "bad" this is but I've done it all season with no ill effects.
(all of these numbers are in Fahrenheit)
My tank runs warmer in the summer (79-81) and colder in the winter (74-76) per reef controller program.
In reality the overall seasonal range is more like 69-82 due to weather. Since I moved my tank in the garage I've noticed that on cold nights there is no way to keep my temps where I want them unless I opt to increase my energy bill by over 30% so this has been an experiment of sorts...
On very cold nights my heaters do not keep up and I've seen temps drop as low as 68 degrees with both heaters running non-stop. Fortunately I'm in california and this is rare but in the summer it does get hot and on most days my 120mm fan can keep the temps in check only allowing them to max out at about 81 but I've seen 82 once or twice.
With that in consideration I've programmed my controller to run the tank hotter in the summer and cooler in the winter in an effort to stabilize the temps as much as possible for days when my efforts can't curb the extreme hot or cold.
Well after 2 summers and now first cold winter in the garage I must say I'm shocked at how little this has affected my tank, fish were fine and maybe a little less active than usual but it didn't stop the clowns from laying eggs and the other fish who chase each other still did their thing as usual. Corals continued to grow at the same rate and showed zero signs of stress. I would have never purposely run a tank down to 70 degrees but I had no idea that a tank can survive at temps that low... If you're wondering, during the coldest week the tank ran in the low 70's for that whole week as the temps weren't climbing enough during the day either so max was about 72-73. Now temps are more normal so I'm hovering around 74-75 every day.