When I ask this question, I am first and foremost trying to gauge the patient's awareness of their condition. You will have some time since you give them their complete exam, so I already have a pretty good idea if it is something like parafunction or occlusal disharmony.
From a Dawson perspective, I always start with the complete exam, which then leads into your full diagnostic records and a full occlusal analysis. A full wear case should never be treated, unless the cause can be identified or all other options have been exhausted and treatment must move forward. (this sentence doesn't seem to flow, but I'm not quite sure what is being conveyed.
When we're discussing single tooth dentistry versus comprehensive or full mouth dentistry, the first thing I think that needs to be determined is, can we treat this person with single tooth dentistry? If not, are they a specialty patient where we have to take more into consideration?