How you set up a tackle rig can create an advantage or a disadvantage. A whip configuration when you add in friction will increases the pull not decrease it.
With just one block, the two configurations are the whip and the runner. The whip configuration gives you no real pull advantage. The runner configuration drops the pull almost 50%.
The whip has the block attached to the place you need to move your weight to, and your rope is attached to the weight and then through the block. With this set up it takes the same amount of pull to move the weight as it would to just attach the rope to the weight and pull it without the block. The whip uses a block only to change the direction of the pull.
The runner set up attaches the rope to where you want to move the weight and the block is attached to the weight. The rope goes through the block and is then pulled. The amount of pull to move the weight now is halved (not counting for friction and what energy the block absorbs). The runner set gives a mechanical advantage.
A block exacts about 10% of force that is applied. (The block uses a little energy when it works)
A block can give a mechanical advantage when rigged right. Any tackle can be rove (rigged) to advantage or disadvantage: the runner is rove to advantage because both parts are pulling the moving block. With the addition of another block the mechanical advantage can go way up.