I've not made any sub-one ohm coils myself; but have seen posts where people say they've made and used 0.8ohm coils. With a fresh battery (4.2V) and a 0.6 ohm coil, you would be
vaping at over 29 watts. Personally, if I go over 6.5 watts my all-day-vape juice (DIY peppermint) starts tasting bad.
Some seem to prefer higher watts for their particular juice or for increased throat hit or just increased vapor. Going below 1 ohm on a coil seems to me to be reaching for something other than a satisfying vape; but then again, I don't vape any juices that require high watts to bring out the taste.
I would caution anyone using sub-one ohm coils to do so only at your own risk.
vaping should not be used to "go one better"; but as an alternative to smoking tobacco. My advice is to build coils at the ohms that give the optimal combination of taste/TH/vapor for your juice, not because Johnny-down-the-street did it

.