The House "Holds" are exclusively utilized to train the decelerator muscles....nothing else. By having stable / strong decelerator muscles, you will / should find velocity gains...... while most train the motion that has to do with forward throwing,....the body (brain) has a safety mechanism in place to limit the speed of the forward throwing motion, to ONLY as fast as the body (decelerator muscles) can slow it down without injury. The better / stronger your decelerator muscles are, the faster the arm will be allowed to move (arm speed).
The "problem" with the way House trains the decelerator muscles is that quite frankly there are much better drills / exercises that address these muscles more effectively, without having to simulate and actual throw (pitch). Injury happens with holds when they are performed without proper technique / instruction / and watchful eyes. A low elbow, altered arm slot, etc. will put undue stress with the heavy weighted implements (weighted balls) and "could" cause injury, or pain. They can be effective (although - again there are other methods better) provided they are instructed, watched, and maintain good form.
Those who may be familiar with Dr. Marshal may remember his very odd drills with pitchers using wrist weights, and somewhat simulating a very slow, more controlled overhead throwing motion....this was where the focus of training decelerator muscles started....House just uses weighted baseballs, and simulates more of an actual full speed pitching motion. I like Marshal's better, however there are many other ways to accomplish the same....reverse throws with 2lbs. / 4 lbs. plyo balls, reverse band pulls, etc.