Moving things can also mean putting them in a new position. Imagine that you need to lift a heavy sack.
If it's too heavy, you could try:
For both choices, there are trade-offs (you owe the friend, instead of one lift you have to do lots of small lifts).
Or you could try:
There's still a trade-off.
Lifting with pulleys, the helper, lets you share the load. You don't have to support the whole weight while lifting, only a single rope. All the ropes share the load: the more ropes, the smaller your share. When there are more ropes, you have to pull more rope through the pulleys to do the lifting.
That's the trade-off for this helper: between how far you have to pull and how hard you pull.