Ailments are contagious, so even if you have good Balance it's possible you could catch them contagiously (at least according to the Moodlets I've had when I've caught them). You can also get them spontaneously (no contact with other Sims needed) when your Balance Metre is Very Imbalanced, so turning off Balance can reduce them by eliminating this method of getting them.
Luck being turned on probably doesn't make much difference. I haven't checked the code to see if having Bad Luck increases the rate, but if that's the case then presumably having Good Luck would also decrease the rate, so that one has the potential to both help and hinder when it's tuned on. You can also take measures to increase (or decrease) your randomised daily Luck level, so it's manageable, to an extent. Turned off it would just give Normal Luck-based chances. Pick whichever you prefer in this case.