Thin Potions

How would they work?

You can make any potion into the thin version by putting dried kelp in a brewing stand with potions at the bottom. It would not be able to work with level II potions and extended potions, for example you could not put in dried kelp to make a thin potion and then put in glowstone to make a level II potion. This would prevent it from being to overpowered.

How would this be useful?

It could be used in tight situations where you might not have enough time to drink a full potion before you die, like falling into lava in the nether and drinking a fire resistance potion.