Very good as it strengthens your throwing arm, but you need to limit how much you're doing it. I really would limit it to as low as 10-15 throws the first time out and then build up as you go.
Set a number, if you don't feel anything, still stop because you don't want to risk over doing it. If you feel something before you reach that number, stop. That's when it becomes a bad drill, when you're overusing your arm and really forcing everything. You start using bad throwing mechanics for both your arm and your body which can lead to injury and bad mechanics in general for the game.
As long as you're throwing correctly and limiting how much you're throwing, it's a good thing, 0 doubt in my mind.
(Even MLB players do this. I know most starting pitchers do it on their middle day of rest)