The bottom of the can is generally left in place, as this yields a stronger stove structure and minimizes spread of fire to combustible material on the ground.
The bottom/side hole may face the wind for more heat or it may be partially covered with scrap metal if the fire is too hot.
Use of a Buddy Burner allows the use of such less-volatile liquid fuels as rubbing alcohol, kerosene, or wax.
Reusing containers originally holding paints and other types of chemicals may be injurious to the health of the user if the can is not properly cleaned and decontaminated.
While dry twigs and other natural fuels may have low risks, the use of other materials such as pressure treated lumber may lead to exposure to carcinogens of various kinds.