There is an on-going debate in baseball circles about the value of long-tossing.
I know it's shocking to think that anything in baseball is debated.
(Yes, that's sarcasm if you weren't sure.)
Some love it, some hate it. This post does not get into that argument.
I'm in the "love long-tossing" camp and it's ok if you are not.
I saw a great MLB Network Diamond Demo on long-tossing (2nd half of clip) or what Mitch Williams calls "long-throwing." I like and agree with his explanation on the difference in terminology. In the Demo, Mitch mentions "walking into the throw." I have always prefered the method used by Roy Halladay in the following YouTube clip. He takes a step forward with his left foot but then hops behind with his right foot, steps, and throws. I like this better because it keeps the pitcher's front side closed longer. A good habit for a pitcher!
The next clip shows a long-tossing routine which includes what they call the "stretching out" phase and the "pulling down" phase. Some people see value in launching a high arching ball to stretch out and strengthen the arm but, like Mitch Williams, I don't like the idea of lifting the front side too much and leaning back to do it. That's not what pitchers do in a game so I'm reluctant to have pitchers do it in practice. I believe there is more value in throwing balls that are able to get to your partner on a hard line drive rather than a high arching one that travels 300+ feet. For most players, that might require maxing out at around 150-200 feet depending on your arm strength. I guess that means I like their "pulling down" phase better.
Over time, pitchers usually develop a long-tossing/long-throwing routine that works best for them.