Final answer:
Simple machines cannot be ideal because they cannot create energy, only transform it, and real-world limitations like friction reduce efficiency. They offer mechanical advantage by allowing less force to be applied over a greater distance while conserving work.
Step-by-step explanation:
No simple machine is ideal in practice due to energy conservation laws and the presence of factors like friction and wear. Despite the energy put into a machine, it cannot create additional energy, which implies that the work output can never exceed the work input. Consequently, efficiency is never 100%, and some energy is always transferred to non-useful forms such as heat.
Simple machines are quite useful because they can change the force required to do a certain amount of work. By using a machine, one can reduce the force one must exert, though this often means applying the force over a longer distance, as the product of force and distance must remain constant (as work is conserved). The mechanical advantage (MA) of a simple machine, which is the ratio of output to input force, typically defines how much easier the machine makes a task.