The bulbocavernosus muscles (BC) wrap around the bulb of the penis (the end of the corpus spongiosum - CS) and are the primary muscles behind the force of ejaculation. Since they surround the end of the CS, any contraction would also contribute to a stiffer erection. There are involuntary contractions throughout the act of intercourse and you can, of course, contract them yourself. If they have been exercised then, just like any other muscle, their strength will be greater. This will give “stronger” erections and more forceful ejaculations. Kegels are the means of exercising the BC muscles.
A reverse Kegel is an attempt to relax the BC. It’s sort of like relaxing to urinate without actually releasing the bladder neck sphincter and letting urine flow. Doing this at ejaculation usually results in semen “flowing” rather than spurting because you’re consciously controlling the muscle that causes the ejection of semen at climax. This is different from constantly contracting the BC at the time of orgasm to prevent ejaculation which is the method used for male multiple orgasm. The continuous, conscious contraction fatigues the muscle and allows only a weak ejection of semen or none at all (with practice).
So magnumforce, you do use the BC in a variety of ways whether you intend to or not and having stronger, well exercised muscles (by doing Kegels) will make them work better no matter what you’re trying to achieve. I recommend Kegels as a normal part of creating optimal sexual health in men. One hundred three second contractions per day is enough. No need to go overboard.