My experience is Slime will seal small circular punctures such as from a tack or a nail, but the tube won't hold full pressure and it leaves a mess inside the tire. It does make the tube difficult to patch, which can be a problem on a longer ride if you've had more than one flat.

I see the merit in only pulling off part of the tire to patch the tube, which makes a good deal of sense for someone who needs to get back on the bike as quickly as possible. I've had the misfortune that there were two places in the tube that needed patching and I missed the second puncture even after removing the tube. So I tend to perform the ritual of removing the tube entirely and either patching it or replacing it as that seems to work best for me.