I feel like they're overall burdensome unless they are a plot point (which they may be soon in my game; the god of evil lycanthropes and the god of undeath and disease are in a little war right now...). Most of the time all I have is "minor illness" as one of the Terrain Hazard options on my random encounter tables for wilderness travel. Examples I have noted to use are, "sunburn, allergy to local plants, poison ivy/oak, rash from insect bites, etc.".