Only get the doctor checkup if your peeps' health is below 50%. Be careful though... I had 3 peeps in 1 family "weak" "extremely weak" and "a bit weak" and none of them had anything wrong, they were just hungry. I wasted $525. Oops.
I would completely agree with this when just beginning a family as money is tight, but it can be a good idea to use it whenever your people are sick once money is no longer an issue.

I earned both of the higher trophies for illness because I used the doctor checkups on what seemed minor illnesses. If money is no longer a problem, $175 is cheap compared to the amount of hand gel and vitamins needed to bring health back quickly.
