Well really, I don't. I'll use a flash during the reception at a wedding to light for the people and their skin. But in situations where I am not going to use a flash, if I need to - yes I'll shoot over 1000 ISO.
Why? Because it is easier to edit an image with a higher ISO if the exposure is already on point in camera. When you've lifted your ISO but you haven't done it far enough, what happens in post when you push the exposure 2-3-4 stops higher is you end up with a significantly more noisey image than if you'd just shot the image at 1500 or 2000 ISO or even 4000+ ISO, instead of 800.
So my rule of thumb is: Open my Fstop up as much as I can, so that means shooting 1.2, 1.4, 1.6 what ever the smallest number is on my lens.
Bring my shutter down to 1/200th of a second or even 1/160th of a second if the subject and myself are both still.
THEN change the ISO. I'll put my ISO up as far as I need to in camera to light the subjects skin well.
Then we edit that image, we barely have to lift the exposure any further and the image is less grainy than the alternative. Lightroom has these handy tools like noise reduction and sharpening to help you polish the image and reduce the grain if you prefer a less grainy look. AND then there are even softwares like Topaz Labs that you can use for sharpening or noise removal as well!
So can you tell the difference in these images? Which ones have flash and which don't!