I'm a so- so advocate of long toss, not that it's a bad thing, but the mentality that is associated with it (long toss that is.)
In a professional sense, let me paint this picture to you. Time is money- period. Everything revolves and evolves around the buck. So, the cardinal rule that I use to use is - don't get hurt, do something ... anything .. that'll improve your workability and dependability, but don't over do it.
I would use long toss for various reasons, but in every case, as a simple game a catch to keep the juices flowing and the muscles moving. I would never expect velocity to improve, nor control to improve, nor would I expect a man to go an extra inning or two, improve his mechanics or even anything close. I would use long toss to simply keep the body use to certain movements - but not so disciplined as to warrant video and such. A simple game of catch over a reasonable distance - and not trying to impress the ladies with a moon launch either.
Also, I knew the way every pitcher that I was responsible for moved, turned, made his stride, and so forth. Therefore, long toss was not pitching done upright, but rather a simple game of catch to keep things moving.
Now here's one of the most important things that I used long toss for:
I'd also look for restrictions of the body during a long toss session, to signal me that a man isn't moving the way he should. Now I've got to qualify myself on that last sentence, and in a way that's not too belligerent either. So, to come right out with it ... some pitchers can be as dumb as a fence post. They'll get hurt, try and hide it, cover it up with all kinds of wrap and liniment, so on and so forth. As for me and others who have to project and use said pitchers, it makes it difficult to pencil in man, only to find out he's only 65% going in, and even less coming out inning after inning.
I found the best way to long toss is with players that get along great. they'll joke, laugh it up, poke fun at one another, and so on. Basically, a good time out on the grass, tossing the ball around over slightly longer and longer distances - but restrictive distances. Good reminders of the proper point to break the hands, start momentum moving, get the throwing arm up in the cocked position early, rotate the shoulders, turn the core and hips/legs, plant to stride foot firmly ... but don't... repeat... don't over do it. Have a relaxing time reinforcing things that should be taken for granted during live time on the mound - but in a general sense.
As far as the number of tosses, before and after an appearance, go-or-no- go after an injury are all things that should be addressed by a coach who understands the individual pitcher, age, tolerance restrictions, environmental influences, and so forth.