Its not always the bacteria that makes you sick its the toxins they leave behind that the microwave can't kill that make you sick.
I wouldn't go that far but I'll leave stuff in the fridge for over a week and still eat it. I rarely throw left overs away. I'd feel like a terrible person if I threw away a feast because it was 3 days old.
Well, I don't literally feel terrible throwing away food, but I don't do it often. Most Americans throw away much much more food than I do. I literally have some stuff in my refrigerator that's been in there over 10 years!

Some stuff just never seems to go bad. Like I say, I can't remember ever getting sick eating my food. I ignore expiration dates, most of those are just there because they are required to put them there (I think they are required). If it looks and tastes good and doesn't make me sick, why toss it? I bought past date yogurt a lot (don't have source for it now), and it was always fine IIRC.
The best thing about leftovers is it's already prepared. As long as you enjoy it, it's reasonably good for you, isn't going bad, won't make you feel bad, I say go for it.