Chili powder, coriander and caraway seeds all make great substitutions for cumin. Home chefs can swap these directly for the spice in many recipes.
There are several reasons not to eat cumin. It has a strong flavor, and some people don't like the taste. Some people also have allergies to the spice. Substitutions are also necessary in those emergency cases when the cumin supply runs out in the middle of cooking a recipe.
In the case of allergies, some substitutes are not appropriate. Coriander and caraway seeds are related to cumin, so people who have a cumin allergy may also react to these spices. Chili powder is a good alternative for people with allergies. People who dislike cumin may also find that caraway seeds are a poor alternative, as they have a similar taste.