Arghhh. As has been said its very much about individual preferences. 12,800 is way way too noisy for my taste (in the cameras I have)
ISO 12,800 is way, way higher than you'd ever need to go, unless you're shooting in near perfect darkness.
Alternatively, ISO 12,800 is completely acceptable if you're shooting with the
Sony A7s series whose sensors are capable of producing clean shots at those kinds of ISOs and beyond.
When I used to take my M8 out into the night to shoot my constantly moving cats and dogs, I'd only go up to ISO 320 most of the time. ISO 640 was the most I'd go, ever.
These days with my M10, the vast majority of the time (99% of the time) I'd only go as high as ISO 3200. I might go ISO 6400 but that's if I'm shooting at 'exceptionally' dark circumstances (eg. an unlit street where the closest street light is a fair distance away).
I shot a wedding a couple of years ago, it was the end of a very long day, the wedding party had moved to the club for an afterparty. It was dark in there, and I mean daaaaaark. But I still managed to catch a few choice shots of the guests and this photo of the bride and groom. I haven't got the specs of the photo at hand but I'm sure it would've been ISO 1200 with my M240. I stress again, it was freekin' dark in there.
Somebody's uncle was sporting a full Nikon DSLR kit at that wedding, he was all about the flash at that afterparty. I remember him watching me work throughout the ceremony and reception, then he came up to me and said something along the lines of: "hey, I see you're shooting with a couple of
Fuji X100 there... " and then he faltered when he came closer and saw that they were Leicas. :-D :-D :-D