A setting where naturalistic observation would be fruitful is on prison populations. Aside from the subjects being in confinement, it is not always possible to take an inmate to a lab. Unique personalities are often found in prisons, you aren't going to see those same traits in a lab setting, there also may be a safety concern of the researchers if they are studying violent offenders. The researchers want to minimize chances of getting attacked, so keeping their distance would be a wise idea. By studying offenders in a naturalistic setting, you are going to be able to see how their aggressive personality manifests when they are among other inmates. While it may not always involve violence, you might be able to see how dominant someone with violent tendencies is, or whether they are dominant at all. It can be a core feature of naturalistic observational studies to go unnoticed so as not to influence the behaviors of the subjects, you would easily be able to get observations from a far when you are in a prison setting (Hansen & Myers, 2012).
Another type of setting that a naturalistic study would be useful in would be mental hospitals. This would allow you to study the social skills of those affected by mental illness, you would be able to see how someone's mental disorder affects their day to day interactions with other patients. The data that is gathered can then be brought to the head psychiatrist to address whether treatments prescribed to the patient is having any effect. By doing this a discussion can be had whether or not the treatment is working or not, this data will help with gaining insights on whether a medication needs to be changed or a dosage adjusted. Drugs that are used to treat mental illness can have side effects that are undesirable, a naturalistic observational study will help determine if those side effects are problematic for the patient or not. Some side effects can be easily ignored but other side effects can hinder the patient's ability to function. In the case of the latter, insight is needed so a remedy for those side effects can be discussed among the staff of the hospital.