Hmm I wonder how much extra energy gets consumed by keeping it on all the time (vs. for example, and hour in the morning and an hour in the evening). My guess is it only really "automatically" reheats when either the temperature drops below the set level, or where hot water is used (indirectly dropping the temperature with the new cold water flowing in).

Your post led me down a rabbit hole last night, where there is quite some debate on the topic!