I think that, in general, many aquarists tend to keep most species at temperatures that are a wee bit higher than is necessary, although still well within the tolerable range. Worrying about a 2 degree difference only really makes sense when the species in question is already being kept at a temperature that is approaching one of the extremes (high or low) of its "acceptable" range...but it does save money on electricity. If your ambient room temperature is ten degrees below your desired tank temperature...i.e. a very realistic example...and you dial down your tank heaters by only one degree, you have reduced the amount of heating and therefore the required energy to achieve that temp difference by ten percent. Since heating water is far and away the most costly component of maintaining most aquariums, this can be significant.
When breeding, even a couple degrees can make a difference to activity, and also to fry appetite, metabolism and growth rate, so that's an area where I tend to go a bit warmer if I want good growth of young fry. I have a few Goodeid fry which were born at the beginning of this cold season, just before they were moved into the basement where most of them are currently at about 60F, and they show ridiculously slow growth compared to siblings that were born last spring and had an entire warm summer to bulk up.
Finally...google the temperature requirements of a few random species of fish and see what you find. When I see the temperature range is suggested to be "in the low 70's" or "70 - 80 degrees", I tend to think that it might be realistic. But when I see something like "temp: 73.6 - 81.4 degrees F", it makes me wonder how much I trust that source. Did they read another source...likely in degrees C...do a mathematical conversion, and then just slap that number down without thinking about how silly it sounds? Key words there: without thinking. How many times does that happen in the aquarium literature?
Read everything. Don't completely believe anything. Avoid extremes.
