In my many years of travel I have run into some bad horror stories of people being pick-pocketed and robbed but these are very rare. What I hear about more often is people doing dumb stuff and simply having things fall out of their pockets because they were put into awkward positions when crammed into a minivan or bus and then having something fall out of their pockets.
I'm not saying that people never get ripped off when backpacking because they certainly do, but it is probably less likely to happen than if you were back in your own city than it does in a vast majority of the countries around the world or at least to all the ones I have been to and I have been to over 70 of them.
These travel wallets are impractical for day-to-day life but I personally feel as though they are absolutely essential to the backpacking masses and since they cost almost nothing, there is no reason to not get one.
The style that goes around your neck is my favorite kind because they are lightweight, adjustable, and after a little while you don't even notice that it is there. You are never going to accidentally have this fall off of you because the loop is solid, so even if you are a dolt and somehow manage to lose the adjustable clip (which are very strong, mine is 20 years old and still functions) it still can't fall off of you but instead, it'll just swing a bit low.
These are specifically designed to be big enough to hold money, cards, passports, and cash all at once and are even long enough to hold flight tickets. Still though, this doesn't mean that I think you should be walking around all the time with all of this on your person. There is still the chance that you could do something exceptionally stupid like take it off and put it on the chair next to you only to forget that you did so and then leave it behind.
The "belt wallets" I like considerably less because even though the woman in the picture above is in very good shape, most of us aren't and these can be quite uncomfortable if you have a few extra pounds on you. The main reason I don't like these is because of the fact that most of the places I travel to are hot and humid areas and this means that this wallet which is securely strapped to your body and is actually meant to go under your pants, gets sweaty and disgusting after just a short while. Plus people generally are less than enthusiastic about receiving cash that has been sitting next to your crotch while you ambled all around town sweating buckets. It's just kind of gross.
I think that either of these items are a "must have" for all backpackers though because not only does it conceal where your money is and make it very difficult for any would-be thief to pick-pocket you (they'd have to be some sort of special magician to make that happen) but it also drastically reduces the chances of you accidentally dropping it. Once something is attached to your body, it's gonna stay there until you take it off. It seems a bit obvious doesn't it?
In my travels I have met a ton of people that have lost important cards, cash, passports, and other important documents and NONE of these people were using this very inexpensive accessory. So once you begin your backpacking journey, do yourself a favor and pick up one of these - particularly the neck option - before you head out the door to the airport. There are a wide variety of them and most are around $20. There is no reason to go with big name brands such as North Face regardless of the claims they make. It is a very simplistic piece of equipment and I haven't noticed the difference between any of them no matter who manufactured it.
$20 could mean the difference between losing all your important documents or not. Personally, I think it is one of the best travel investments I ever made.