Do you use the auto iso? Why or Why Not???

Last weekend, I went out on a photoshoot with two of my grandchildren. One uses my old GF1 which I gave him and the other used my GH2, and I used my GX1. I had used my camera indoors with my 20mm 1.7 and the iso at 1250. I forgot to reset the iso and consequently my pictures were inferior to theirs. I really do not care about that (actually I want their pictures to be better), but it worries me that when I am on a trip or taking pictures where I will not have a second chance this will happen. I have decided that in the future I am going to use auto iso and put the limit on iso 800. Anything above 800 I will have to set manually. Does this sound like a decent idea to you? What, if any, are the negatives to this?

Thanks,

Hal