There's two drawbacks of the Kekkei Genkai, one of them is dehydration. Using the sludge excessively will cause dehydration of the body, so it's important to drink plenty of fluids before battling. The other draw back of Sludge Release is having comrades near by. Most likely, the comrades are not immune to the poison. Which leads Sludge Release users to use different alternatives on the battle field.