Make mine a .357 a revolver, thank you. Versatility is the main reason, but my handloads in 125 grain destroy .357 Sig ballistics. I get 1600 fps from a 4" barrel. That pretty much puts the lid on the .357 Sig, makes about 700 fpe. Those ballistics are what the .357 was originally intended to do before the big ammo companies neutered their loads from fears of liability lawsuits. I like the revolver and caliber as a back country hiking gun with heavy 158 grain SWC loads and as a small game getter with my 148 grain .38 wadcutter load which shoots into an inch at 25 yards out of my Taurus M66 OR my 6.5" Blackhawk. I've killed deer at 50 yards with that 158 grain magnum load from my Blackhawk. I have an even better, flatter shooting load now consisting of a 180 grain Hornady XTP moving at about 1450 fps from that Blackhawk. That one is very accurate right out to 100 yards. It's only 2" high at 50 and dead on at 100 and with the Blackhawk's iron sights I can put them into 4" off the bench at 100 yards.
You simply can't do all that with the Sig. Yeah, it's a good self defense weapon, but that's ALL it is. If you like the outdoors like I do, the .357 4" revolver is a much more versatile weapon, that is, if you don't wish to own both. I rely on the .38, 9x19mm, and .45ACP with one gun in .380 for CCW self defense, though. My .357s are field guns carried open on a gun belt in a simple uncle mikes camo nylon holster. I gotta admit, though, I often leave the .357s at home and carry my .45 Colt.
i wonder if 100 fps will make any difference for anything...need bigger? get a rifle or a carbine
And, yep, I have a .357 Magnum 20" carbine and ballistics of the round from THAT gun dwarf any handgun. It's a really cool caliber, especially for the handloader. But, unlike a lot of calibers, you don't HAVE to be a handloader to enjoy the versatility of the guns in this caliber or be able to afford to shoot it. I think it's the first handgun round anyone should get. I know it was my first centerfire, though I had .22s before it.