Yeah, they can get into a house by other means. But this is a good way to do it if someone wants to get in without showing forced entry or other obvious signs of a burglary. How often does your wife inventory her jewelry? Someone could break in, take a thing or two, and nobody would even know they were robbed, they might even think they lost it somewhere.
Exactly. The first layer of security is anonymity - recall that the nail that sticks up get hammered down first.
Second rule comes from the jungle - "Look like food and you will be eaten."
Flashy people are usually complacent, and get picked off first. I don't think my wife and I together own $1000 in jewelry, and I know I have considerably less than $500. The only gold I own is my wedding ring, the flashiest thing I own is a 24-hour watch that I bought for $70. I own one suit and one tuxedo (both are worn rarely,) and aren't some stunning designer pieces - they're just a regular grey suit and a regular tuxedo with shawl lapels (probably paid $500 for both of them.) I only paid that much because I took my .45 with me when I got fitted, and had them tailored so they won't print - I may not have a CCW here in CA, but I do in other states, and I could end up going anywhere. I've got family all over.
Bumping may not show any obvious signs of forced entry, but a locksmith who is on his mark can see some small signs (usually misalignment of the strike, caused by impact on the doorknob) if he really looks. How often does that happen? The tumblers will also show "pick marks" (distinctive toolmarks on the tumbler heads) as with picking, but you have to disassemble the lock to see them.
It's also useful with various techniques of forced entry as a distraction - one could gain entry, and make it look as if one has not managed to get in to delay inventorising the contents of the house.
Why have I learned so much about locksmithing and burglary? Simple - I've also helped to secure houses against unauthorised entry, usually for people who are unable to deal with the threat in an expeditious manner on their own (elderly/disabled.) It's a nice skillset to have, and most people don't know how to think like a burglar to do it properly.