Many people choose to add an ADU to their property with the sole purpose of renting it out in order to make a little extra money, which can be a good use of this space. Some cities, counties, and states have regulations regarding how many non-related people may reside on a single property, so you want to check for ordinances like this before you take on any renters. \
Otherwise, there is no reason that you cannot rent out your ADU in order to make some extra money. You can also consider using this space as a temporary rental, such as an Airbnb, in order to get a little income from your unit. \