The real answer to this especially regarding SPS, would require more information.
Generally speaking swings of any kind are considered to be less than desirable, more so with SPS.
But as you can see in previous posts there are plenty of those that have no obvious issues with having temp swings any more than those that don't.
Where a temp swing (or any instability) would truly come into play is ....just how close to the edge do you run your tank?
What I mean by that is, there is a difference between healthy and "fit".
People who train their bodies to have as close to 0% body fat that are wanting an incredibly ripped physique might be "fit" as hell.....but are most certainly not healthy.
Many SPS hobbyists tend to prefer ultra low nutrient systems so that they can get their corals colors to their extreme, which is not always natural, neither is running on the high edge of Calcium and Magnesium for rapid growth.
So, these corals would be considered more "fit" than healthy.
This would also make them less tolerant of swings, as it can be very easy to disrupt the delicate balance that they live in.
It also has to do with, what SPS exactly? Some are more hardy that others, some have no tolerances with swings at all.
All that being said, generally speaking, it would be best to keep temp swings no greater than 2* .....but it's certainly not the Law....