New guy to the area here, but my thoughts -
Berries are a great forage food/snack, though not great for storage or transport in their unprocessed form. Though, jams and jellies are always a favorite, and there's nothing better than a blackberry cobbler. Not sure if they can be dried well, I might have to look into that, unless someone knows the answer? But, easy pickings for some natural sugar and a high moisture content make them great for late afternoons in hot fields.
The most you (usually) have to compete with is birds, so if you have a problem with thievery from animals, a lot of them are going to find less prickly dining. The same can be said for the human element as well - if there's a problem or you want to prepare for the possibility of people raiding your gardens or orchards, blackberries grown around fencing make a great combination to deter all but the most dedicated, or at least funnel them to somewhere you want them to go. All creatures, regardless of if they have four or two legs, will take the path of least resistance, and unless it's life or limb, they're not likely to climb or crawl through a wall of sharp blackberry brambles. And, those same brambles can put some food on the table as well, so your security system can pay for itself. This doesn't work on everything of course, some large animals simply aren't bothered by them terribly (such as cattle), but horses tend to avoid them.
Of course, using them intentionally for this would require some effort in planting and training, or simply cutting away the undesirables and leaving the ones you want, if they volunteer easily in your area. They do, at least where I live, grow wild in abundance to the point of annoyance, but they're remarkably resilient and seem to grow just about everywhere. I can't imagine it would take a lot to grow some to task if desired, though they do tend to underproduce when there is a lack of rain. I have not, however, seen any healthy plants die, even in the worst droughts in the area. Once they're mature, they're almost impossible to kill completely - even being cut down or aggressively trimmed will only beat them back until the next year. Of course, the trick is getting them to mature, so if you're having to grow them from seeds, there might be a venture in that, but I've never attempted it.
