why would vacuoles be useless in animal cells?

Animal cells do have vacuoles but you are essentially correct. The main function of the vacuole in a plant is to maintain tugor pressure. Tugor pressure is "kept in check" so to speak by the cell wall in plants. Animal cells do not experience turgor and do not have a cell wall. If a large vacuole swelled to increase pressure in a animal cell, the cell could burst because the cell membrane is not thick and strong like the cell wall.

Since we don't have a vacuole, let alone a large central vacuole, I have no clue. But, I know that plants use them for

* keeping harmful materials found in cell

* removing unwanted debris

* containment of waste products

* maintaining an acidic internal pH

* containing small molecules

* getting rid of unwanted substances from the cell.

* shape