A very simple weight-lifting is shown in Fig. 4-1. This machine lifts three units "strong". We place three units on one balance pan, and one unit on the other. However, in order to get it actually to work, we must lift a little weight off the left pan. On the other hand, we could lift a one-unit weight by lowering the three-unit weight, if we cheat a little by lifting a little weight off the other pan. Of course, we realise that with any actual lifting machine, we must add a little extra to get it to run. This we disregard, temporarily. Ideal machines, although they do not exist, do not require anything extra.
This may be already answered by @mmesser314 here, but I want ask the question from a different point of view.
During the first part of the paragraph, we are told that "little weights" must be "lifted off" the left and the right pans to get the machine to "actually work". Assuming that in this context lift off = remove, that makes sense. But then we are abruptly told that we should add a "little extra" if we want to use an "actual" lifting machine. I assume that actual = in real-life and extra = additional weight or force.
So which one is it if the machine is not ideal - do we add or remove weights for it to work? Do we do both? First "lift off" a little weight, let the lifting and the lowering occur and add a "little extra" to do the reverse operation?