Cost savings? Unaccurate factory loads? Do you shoot a gun that's ammo is expensive to buy or find? Want to shoot a bullet that isn't offered in factory loads (like a 168gr A-Max for the 7mm-08 Rem.)?
Cost savings. I always wanted to do it but I shot rifles very seldom (sight-in and hunting). When I turned 21 and started buying handguns I shot a bit more and really started researching all the ins and outs. It was an on again off again affair. Never really took the plunge until about a year ago.
Now I'm off to a good start loading every cartridge I shoot plus cast my own bullets. I very rarely buy bullets. I usually only buy primers and powder, trade for brass.
I wish I got into it sooner. Now I can afford to shoot guns I wanted to because I can afford to feed them. Factory 375 H&H Magnum cost about $2/rd. I load them myself for about 17¢/rd. Quite a savings there- 91.5% savings.
How 'bout you?