I use slightly cooler water when I do water changes: it doesn't affect the my reds, but the cories in their tank become really horny because of that (would be nice if they spawned in my piranha tank, but so far no luck yet...)
In general, a temperature mismatch of one or two degrees is nothing to worry about (in fact, breeders do use much cooler water to trigger breeding behaviour with a number of tropical fish: mimicking the rainy season), but for your average weekly water change, try to match as closely as possible.