I find auto ISO very useful and use it nearly all the time. Unless you use you camera in full manual mode, it is always going to make one decision for you, either ISO, shutter speed or aperture. I nearly always use manual exposure mode but auto ISO so I have full control over aperture and shutter speed, and if I can see the ISO going beyond where I want I can easily change the shutter or f number. I think on most cameras they are the easiest and quickest things to adjust - on my cameras certainly changing the ISO is the fiddliest.