Couple things. A lot of times the front sight is too short to get a proper zero. Especially if you shoot long-range, heavy for load bullets and slow powder with a magnum charge.
Sometimes, you just want to different shape sight. Me personally, I do not like the ramp sight Ruger installed on their guns. My eyes do not do well with that style site in the sunlight. I prefer a vertical face on my front sights. Similar to a post, or a Patridge style. These sights allow you to create whatever shape front sight you want.
Yeah, my local smith put one of these on a 45 Blackhawk for me back in the '80s, looks nice, works perfect, same brand, Bowen. Otherwise I could not get the Ruger on target at 25 yards with the sight that came on the gun.