Nothing makes my heart soar like watching dogs run free. I completely get the whole "leash" thing but it is most definitely restricting. When I was in CA I was constantly searching out new spots to sneak an off leash run. My favorite spots are the ones that no one or very few people know about. Sauntering around while my dogs run at full speed is a very rewarding activity; I always leave feeling like "job well done." Dogs need to run, full out, top speed, pelting, bolting and dodging around.
A full out free run probably does more for their emotional well being than their physical. I know that it fills me with such joy that I don't know who it's better for. Having been plagued with ticks now here mid winter in Connecticut I hit the beach where the dogs are allowed to run free until March 31st. No ticks on the beach, or not that I've seen yet. Once March 31st has passed, then that's it, not one canine foot is even allowed in the park after that (shrugging shoulders).
We've yet to run into any problem dogs other than the one bully last week. All the dogs have been cordial and friendly; they are all there for the same reason, fun.
Running free is definitely the best way to accomplish some quality socializing. Leash issues not only restrain a dog from fully interacting with other canines; but they also create all sorts of behavior "issues." Most problems are caused by the lack of freedom, they cannot move away or go to see. A leash also changes how a behavior is displayed and perceived. The leash causes physical changes, a look see can seem like a lunge; the holding back is the big problem. This is why running free is so very important, especially with young dogs.