It's a sad day that SR4759 is being discontinued. It and, to a lesser extent, SR4227, are the only smokeless powders that emulate the bullet obturation feature of blackpowder. And despite Hodgdon's claim that other powders can replace the discontinued powders, this is definitely not true in the case of 4759.
Bullet obturation is when the base of a lead bullet gets slammed by the shockwave of the burning powder that it gets slightly shortened in length and expanded in diameter. This cause the bullet to expand into the grooves in the bore, making a better gas seal and contributing to accuracy. 4759 and 4227 are the only smokeless powders that can do this with soft lead alloys, giving flexibility to those who cast their own bullets but don't want to use blackpowder. 4759 is also a pretty easy replacement for blackpowder (as used in cartridges, not muzzleloaders), the general rule of thumb being that it can be used as a substitute on the order of 1:3, meaning 60 grains of blackpowder can be replaced by 20 grains of 4759.
In addition, despite a lot of warnings from safety nazis and squeamish people, it was common for blackpowder cartridge shooters to use a few grains of 4759 at the base of their cartridge to get cleaner ignition and burning, causing less fowling. This was very common at one time and has decades of successful use. This practice went by the wayside for sports, as the NRA BPCRS outlawed the practice because of "safety issues". I don't know what CASS/SASS says about it. But some blackpowder cartridge hunters still use 4759 to get cleaner burning blackpowder cartridges.
At some point it won't matter, since lead bullets will eventually be outlawed anyway and no one will hunt with blackpowder cartridges.