Originally posted by PixelGeek I just read my camera's manual and decided that auto ISO is evil.
Much depends on the type of shooting you do. I find TAv mode very handy for the kind of shooting I do. I want to control aperture and shutter speed, but I can tolerate a little variance in ISO to deal with changes in ambient light that might occur while I'm actively shooting.
It's very handy when you're doing near-macro shooting of subjects that don't necessarily hold still, and can be scared off if you start moving your hands around on the camera body to make adjustments. If you're in position, and working your subject, and a cloud passes overhead, or a change in magnification requires an adjustment in exposure, it's handy to have the camera compensate without messing with your chosen aperture/shutter speed. With this kind of shooting, I used to shoot 100% manual when I shot film, then mostly in Tv with my K200D, but I like using TAv on my K30. I still keep an eye on what ISO the camera is setting. It works for me far more often than it spoils a shot. If my camera body had poor high ISO performance, I'd probably be less inclined to use it.
Admittedly, that's a somewhat specialized use case. For other situations, TAv may not be my preferred mode. That's the nice thing about having all these different modes on your DSLR - you can try different things and find which mode works best for you in different situations.
Personally, I've never been able to wrap my head around P mode. I just don't get it. But I'm sort of manual oriented, and I've never really spent much time trying to work out how I'd use that mode in the context of my own shooting ( my old film cameras didn't have it ). I see that other people do use it, so I figure there must be something I'm missing. I do not conclude that it is "evil".