Only Federation ships have them. Most do, anyway. Miranda, Constellation excepted, maybe a couple of others. But nobody else's ships have them. We've seen Romulan, Klingon, Vulcan, Cardassian, Breen, Dominion, Kazon, etc. with no sign of this particular feature. Yet Federation ship designers are so intent to include them that they squeeze them in on almost every ship they come up with, even when the placement seems awkward or ineffective (Sabre, Steamrunner classes being the worst offenders). If I understand correctly the device is used to deflect meteoroids, space debris, etc. away from the ship. But the fact that nobody else in the galaxy uses them makes it seem like a not-so-essential piece of technology Other than deux ex machina resolutions to end an episode, I mean.