Syncrasy - Sports photographers put the names of their subjects in the caption and, depending on the agency they work for, maybe the headline. Properly capitalized in both places. Keywords serve a different purpose. And in this case, the "database" actually is the metadata on the files. (That's the beauty of it). The index is just a tool to make searching faster. It's not the data.
I just stopped and figured. In my decade or so as a daily picture editor, I executed over 125,000 searches. (Real, not repetitive. Too many of those to even guess at.) I used case sensitive searching maybe a half dozen times. And probably didn't need to then. Case sensitive searches are dangerous. They do stupid things. If you are searching for "flying", for instance, a case sensitive search will fail if the word begins a sentence. That's like shooting yourself in the head.
Hayo - I actually have searched for Barbara Bush and not in a classroom. In this particular example, since "Barbara" and "Bush" are proper nouns, a case sensitive search could be acceptable. But hardly necessary. The risk if you do it without case sensitivity is that "barbara AND bush" might hit "Barbara Smith tends her rose bush." You won't get every ol' rose bush picture because there were two terms in the search - "barbara" and "bush". There weren't many/any Barbara Smiths with bushes, so there wasn't really be much noise. (And I was working in a collection with over two million assets.) And what if the search was "Barbara AND Bush AND charity"? That would fail if "charity" started a sentence.
On the other hand, even in this rare case where it won't shoot you in the foot/head, case sensitivity doesn't eliminate any risk. Barbara Smith can still be a very dangerous woman. A sloppy person is at risk of running the wrong Barbara, rose bushes or no. A "Barbara AND Bush" search, case sensitive or not, can still bring back a day-ruining return. "Barbara Jones speaks to Edward Bush" will return for that search. If case sensitivity made the editor who did that search feel more secure, it certainly wasn't doing him or her a favor.
Where a case sensitive search CAN be of help (0.00048% of the time, if my experience is typical) is to filter out an overbroad return. If you get flooded with rose bushes, as I said, You CAN in PM+ filter your return with a case sensitive search using Find. But that only works if you don't accidentally exclude valid returns in the first place.
I hate to be strident here, but really. Professional librarians can sometimes use case sensitivity to good effect. For the rest of us, it's just a dangerous weapon we shouldn't touch.