My temperature consistently hovers around 96 degrees. (Yes, I'm also usually cold.) That's whether I take it at the doctor's office or with my $10 Walgreens thermometer at home. I'm told it's normal to run colder as you get older, so I'm not worried about it, but I have temp tracking turned on because it's helpful for for sleep tracking data in AutoSleep and Health and overall wellbeing as others have mentioned. My temperature stays pretty steady whether I'm sleeping or awake, so if there was a prolonged period of higher temperature, the watch would definitely notice and alert me.
I don't know, I think it's a useful function even if you don't need cycle tracking.